Methods for forming silicon-silicon oxide-carbon composites for lithium ion cell electrodes

ABSTRACT

Composite silicon based materials are described that are effective active materials for lithium ion batteries. The composite materials comprise processed, e.g., high energy mechanically milled, silicon suboxide and graphitic carbon in which at least a portion of the graphitic carbon is exfoliated into graphene sheets. The composite materials have a relatively large surface area, a high specific capacity against lithium, and good cycling with lithium metal oxide cathode materials. The composite materials can be effectively formed with a two-step high energy mechanical milling process. In the first milling process, silicon suboxide can be milled to form processed silicon suboxide, which may or may not exhibit crystalline silicon x-ray diffraction. In the second milling step, the processed silicon suboxide is milled with graphitic carbon. Composite materials with a high specific capacity and good cycling can be obtained in particular with balancing of the processing conditions.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of copending U.S. patent applicationSer. No. 13/917,472 filed Jun. 13, 2013 to Anguchamy et al., entitled“Silicon-Silicon Oxide-Carbon Composited for Lithium Battery Electrodesand Methods for Forming the Composites,” incorporated herein byreference.

GOVERNMENT RIGHTS

Development of the inventions described herein was at least partiallyfunded with government support through U.S. Department of Energy grantARPA-E-DE-AR0000034 and California Energy Commission grant ARV-09-004,and the U.S. government has certain rights in the inventions.

FIELD OF THE INVENTION

The invention relates to high capacity silicon based negative electrodeactive materials for lithium ion batteries. The invention furtherrelates to methods of forming the materials and batteries incorporatingthe materials.

BACKGROUND OF THE INVENTION

Lithium batteries are widely used in consumer electronics due to theirrelatively high energy density. For some current commercial batteries,the negative electrode material can be graphite, and the positiveelectrode materials can comprise lithium cobalt oxide (LiCoO₂), lithiummanganese oxide (LiMn₂O₄), lithium iron phosphate (LiFePO₄), lithiumnickel oxide (LiNiO₂), lithium nickel cobalt oxide (LiNiCoO₂), lithiumnickel cobalt manganese oxide (LiNiMnCoO₂), lithium nickel cobaltaluminum oxide (LiNiCoAlO₂) and the like. For negative electrodes,lithium titanate is an alternative to graphite with good cyclingproperties, but it has a lower energy density. Other alternatives tographite, such as tin oxide and silicon, have the potential forproviding increased energy density. However, some high capacity negativeelectrode materials have been found to be unsuitable commercially due tohigh irreversible capacity loss and poor discharge and recharge cyclingbelieved to be related to structural changes and anomalously largevolume expansions, especially for silicon, that are associated withlithium intercalation/alloying.

New positive electrode active materials are presently under developmentthat can significantly increase the corresponding energy density andpower density of the corresponding batteries. Particularly promisingpositive electrode active materials are based on lithium richlayered-layered compositions. In particular, the improvement of batterycapacities can be desirable for vehicle applications, and for vehicleapplications the maintenance of suitable performance over a large numberof charge and discharge cycles is important.

SUMMARY OF THE INVENTION

In a first aspect, the invention pertains to a composite materialcomprising processed silicon suboxide and graphitic carbon. Generally,the composite material has at least a portion of the graphitic carbon ingraphene sheets. In some embodiments, the composite material has a BETsurface area from about 5 m²/g to about 35 m²/g and a discharge capacityof at least about 800 mAh/g at a rate of C/20 discharged from 1.5V to0.005V against lithium metal.

In further aspects, the invention pertains to a composite materialcomprising processed silicon suboxide and from about 0.5 weight percentto 20 weight percent graphitic carbon, in which at least a portion ofthe graphitic carbon is in graphene sheets. In some embodiments, thematerial has a discharge capacity of at least about 800 mAh/g at a rateof C/20 discharged from 1.5V to 0.005V against lithium metal, and thematerial has a 50th cycle discharge capacity that is at least about 87%of the 5th cycle discharge capacity when cycled against lithium from1.5V to 0.005V at a discharge rate of C/3.

In additional aspects, the invention pertains to a method for forming acomposite material comprising processed silicon oxide and graphiticcarbon at least a portion of which is in graphene sheets, the methodcomprising performing high energy mechanical milling of graphite powderwith reduced silicon oxide material having a BET surface area from about2.5 m²/g to about 20 m²/g and a D50 volume average secondary particlesize of no more than about 10 microns, to form the composite material.

In other aspects, the invention pertains to a lithium ion secondarybattery comprising a positive electrode, a negative electrode, aseparator between the positive electrode comprising a lithium metaloxide and the negative electrode and an electrolyte comprising lithiumions. In general, the negative electrode comprises a composite materialcomprising processed silicon suboxide and graphitic carbon in which atleast a portion of the graphitic carbon is in graphene sheets. Thebattery can have at a discharge rate of C/3 at the 50th cycle a positiveelectrode specific capacity of at least about 150 mAh/g and a negativeelectrode specific capacity of at least about 750 mAh/g when dischargedfrom 4.5V to 1V.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram of a pouch cell battery havingapproximate rectangular parallelepipeds configuration.

FIG. 1B is a schematic diagram of the pouch cell battery of FIG. 1A withthe pouch enclosure, battery core, and pouch cover of the battery takenapart and illustrated separately.

FIG. 1C is an illustration of a perspective view of the sealed batteryof FIG. 1B with the pouch cover at the bottom.

FIG. 1D is a sectional view of the battery of FIG. 1C viewed along thed-d line.

FIG. 1E is a schematic representative illustration of a battery corethat comprises three negative electrode structures, three positiveelectrode structures, and five separators.

FIG. 2 is a graph displaying plots of scattering angle versus intensityobtained from X-ray diffraction analysis of silicon oxide particlepowder and of processed silicon suboxide composites samples preparedwith different milling parameters.

FIG. 3 is a graph displaying plots of scattering angle versus intensityobtained from X-ray diffraction analysis of graphite (lower panel),silicon (middle panel) and processed silicon suboxide-graphitic carboncomposites prepared with different milling times (top panel).

FIG. 4 is a TEM image of a processed silicon suboxide-graphitic carboncomposite.

FIG. 5A is a TEM image of the composite depicted in FIG. 4 , taken atlower magnification.

FIG. 5B is a TEM image of the composite depicted in FIG. 5A, taken atlower magnification.

FIG. 6 is an enlargement of a portion of the TEM image depicted in FIG.4 .

FIG. 7A displays a portion of the TEM image depicted in FIG. 6indicating the location at which EDS analysis was performed on thecorresponding sample.

FIG. 7B displays an EDS mapping of carbon concentration in the processedsilicon suboxide-graphitic carbon composite displayed in FIG. 7A.

FIG. 7C displays an EDS mapping of oxygen concentration in the processedsilicon suboxide-graphitic carbon composite displayed in FIG. 7A.

FIG. 7D display an EDS mapping of the silicon concentration in theprocessed silicon suboxide-graphitic carbon composite displayed in FIG.7A.

FIG. 8 is a graph displaying plots of cycle number versus specificcharge and discharge capacities of two half-cell batteries, one batterycomprising a commercially obtained silicon composite electrode and onebattery comprising a processed silicon suboxide-graphitic carboncomposite electrode.

FIG. 9 is a graph displaying specific charge and discharge capacities ofa full cell battery comprising a processed silicon suboxide-graphiticcarbon composite electrode.

DETAILED DESCRIPTION

High energy mechanical milling (HEMM) has been found to be effectiveunder appropriate conditions to form composites of processed siliconsuboxides and graphitic carbon with graphene sheets with surprisinglystable cycling and a high cycling capacity. The milling generally isperformed in two steps to achieve the desired material. The firstmilling step comprises high energy mechanical milling of siliconsuboxide, e.g. SiO, and a second milling step involves the high energymechanical milling of a blend of the product of the first step andgraphite. In the first step, particle size can be reduced, and siliconsuboxide can be chemically modified through high energy mechanicalmilling to form processed silicon suboxide. Chemical processing ofsilicon suboxide powders with mechanical forces can be used to formnanoscale elemental silicon, but the degree of chemical processing canbe controlled to obtain desired performance of the ultimate processedsilicon oxide-graphitic carbon composite material. The high energymechanical milling of the processed silicon suboxide with graphite caneffectively exfoliate significant portions of the graphite into graphenesheets to form a desirable composite material. The processed siliconoxide-graphitic carbon composites exhibit good cycling performance athigh specific capacity in a lithium ion battery. The processed siliconsuboxide-graphitic carbon composites are a useful negative electrodeactive material for lithium ion batteries.

Silicon based active materials can exhibit high specific capacities inlithium based batteries, but the materials generally exhibit largevolume changes with incorporation and release of lithium into and fromthe material. The large volume changes have been associated with anundesirably rapid loss of capacity with cycling. The formation ofnanoscale silicon active materials has provided some stabilization ofthe material with respect to cycling. Also, the formation of compositeswith electrically conductive components, e.g., blended and/or coatedcomponents, has also been found to provide some stabilization. Thecomposite materials herein provide desirable high specific capacitiesand good cycling stability. The exfoliated graphene sheets seem toprovide improved performance based on electrical conductivity andstabilization of the cycling nanoscale silicon material forming in situ.The graphitic material can be included in relatively low amounts toaccomplish the stabilization objectives without adding excessive weightthat can decrease overall specific capacities of the composite material.

Lithium has been used in both primary and secondary batteries. Anattractive feature of lithium metal for battery use is its light weightand the fact that it is the most electropositive metal, and aspects ofthese features can be advantageously captured in lithium-based batteriesalso. Certain forms of metals, metal oxides, and carbon materials areknown to incorporate lithium ions into its structure throughintercalation, alloying or similar mechanisms. The positive electrode ofa lithium based battery generally comprises an active material thatreversibly intercalates/alloys with lithium, e.g., a metal oxide.Lithium ion batteries generally refer to batteries in which the negativeelectrode active material is also a lithium intercalation/alloyingmaterial.

The batteries described herein are lithium based batteries that use anon-aqueous electrolyte solution which comprises lithium ions. Forsecondary lithium ion batteries during charge, oxidation takes place inthe cathode (positive electrode) where lithium ions are extracted andelectrons are released. During discharge, reduction takes place in thecathode where lithium ions are inserted and electrons are consumed.Similarly, during charge, reduction takes place at the anode (negativeelectrode) where lithium ions are taken up and electrons are consumed,and during discharge, oxidation takes place at the anode with lithiumions and electrons being released. Unless indicated otherwise,performance values referenced herein are at room temperature, i.e.,about 23±2° C. As described below some of the testing of the siliconbased active materials is performed in lithium batteries with a lithiummetal electrode or in lithium ion batteries. If the silicon basedelectrodes are placed in a lithium battery with a lithium foil counterelectrode, the silicon based electrode effectively is a positiveelectrode for the corresponding battery even though the electrodefunctions as a negative electrode in a lithium ion battery.

The word “element” is used herein in its conventional way as referringto a member of the periodic table in which the element has theappropriate oxidation state if the element is in a composition and inwhich the element is in its elemental form, M⁰, only when stated to bein an elemental form. Therefore, a metal element generally is only in ametallic state in its elemental form or an appropriate alloy of themetal's elemental form. In other words, a metal oxide or other metalcomposition, other than metal alloys, generally is not metallic.

Elemental silicon has attracted significant amount of attention as apotential negative electrode material due to its very high specificcapacity with respect to intake and release of lithium. Silicon forms analloy with lithium, which can theoretically have a lithium contentcorresponding with more than 4 lithium atoms per silicon atom (e.g.,Li_(4.4)Si). Thus, the theoretical specific capacity of silicon is onthe order of 4000-4400 mAh/g, which is significantly larger than thetheoretical capacity of about 370 mAh/g for graphite. Graphite isbelieved to intercalate lithium to a level of roughly 1 lithium atom for6 carbon atoms (LiC₆). Also, elemental silicon, silicon alloys, siliconcomposites and the like can have a low potential relative to lithiummetal similar to graphite. However, silicon undergoes a very largevolume change upon alloying with lithium. A large volume expansion onthe order of two to three times of the original volume or greater hasbeen observed, and the large volume changes have been correlated with asignificant decrease in the cycling stability of batteries havingsilicon-based negative electrodes.

As with silicon, oxygen deficient silicon oxide, e.g., silicon oxide,SiO_(x), 0.1≤x≤1.9, can intercalate/alloy with lithium such that theoxygen deficient silicon oxide can perform as an active material in alithium based battery. The oxygen deficient silicon oxide canincorporate a relatively large amount of lithium such that the materialcan exhibit a large specific capacity. However, silicon oxide isobserved generally to have a capacity that fades quickly with batterycycling, as is observed with elemental silicon. The processed siliconsuboxides described herein may take a ranges of compositions with someembodiments exhibiting more or less elemental silicon and/or siliconsuboxide compositions, which can exhibit relatively high reversiblespecific capacities.

When lithium ion batteries are in use, the uptake and release of lithiumfrom the positive electrode and the negative electrode induces changesin the structure of the electroactive material. As long as these changesare essentially reversible, the capacity of the material does notchange. However, the capacity of the active materials is observed todecrease with cycling to varying degrees. Thus, after a number ofcycles, the performance of the battery falls below acceptable values,and the battery is replaced. Also, on the first cycle of the battery,generally there is an irreversible capacity loss that is significantlygreater than per cycle capacity loss at subsequent cycles. Theirreversible capacity loss (IRCL) is the difference between the chargecapacity of the new battery and the first discharge capacity. Theirreversible capacity loss results in a corresponding decrease in thecapacity, energy and power for the battery due to changes in the batterymaterials during the initial cycle.

Silicon based materials generally exhibit a large irreversible capacityloss. In some embodiments, the battery can comprise supplementallithium, which can compensate for the first cycle the irreversiblecapacity loss of the silicon based materials as well as to stabilize thecycling of the battery. The supplemental lithium can replace some or allof the active lithium removed from the cycling as a result of theirreversible capacity loss of the silicon based material associated withfirst cycle changes in the silicon based active material. In atraditional lithium ion battery, the lithium for cycling is suppliedonly by a positive electrode active material comprising lithium, forexample, a lithium metal oxide. The battery is initially charged totransfer lithium from the positive electrode to the negative electrodewhere it is then available for discharge of the battery. Supplementallithium results from a supply of active lithium other than the positiveelectrode active material. It has also been found that supplementallithium can be very effective for the stabilization of lithium rich highcapacity positive electrode active materials. See, published U.S. patentapplication 2012/0107680 to Amiruddin et al., entitled, “Lithium IonBatteries With Supplemental Lithium,” (hereinafter “the '680application”) incorporated herein by reference. Thus, good cycling hasbeen obtained for realistic lithium ion batteries with supplementallithium to have relatively high specific capacities. Supplementallithium, for example, can be supplied by elemental lithium, lithiumalloys, a sacrificial lithium source or through electrochemicallithiation of the negative electrode prior to completion of the ultimatebattery. The use of supplemental lithium in lithium ion batteries withsilicon based negative electrode active material is described further inpublished U.S. patent application 2011/0111294 to Lopez et al. (the '294application), entitled “High Capacity Anode Materials for Lithium IonBattery,” incorporated herein by reference.

Silicon suboxide active materials exhibit relatively high proportionalIRCL and cycling instability, while providing a lower specific capacitythan elemental silicon. The reduction of silicon suboxide to elementalsilicon has been accomplished with a reducing metal, and the resultingnanostructured porous silicon has promising lithium cycling properties,as described in copending U.S. patent application Ser. No. 13/354,096 toAnguchamy et al., now U.S. Pat. No. 9,139,441, entitled “Porous SiliconBased Anode Material Formed Using Metal Reduction,” incorporated hereinby reference. Similarly, silicon polymers and other silicon compositionshave been reduced using metal reducing agents or organic reducing agentsto form elemental silicon enriched silicon-silicon oxide-carboncomposites as described in copending U.S. patent application Ser. No.13/864,212 to Han et al., now U.S. Pat. No. 10,020,491, entitled“Silicon-Based Active Materials for Lithium Ion Batteries and SynthesisWith Solution Processing,” incorporated herein by reference. Asdescribed herein, high energy mechanical milling is described to modify,and possibly reduce, silicon suboxide to form a material with desirableelectrochemical properties.

The milling of SiO with graphite is reported in U.S. Pat. No. 6,638,662to Kaneda et al. (hereinafter Kaneda patent), entitled “LithiumSecondary Batteries Having Oxide Particles Embedded in Particles ofCarbonaceous Material as a Negative Electrode-Active Material,”incorporated herein by reference. The Kaneda patent does not describethe formation of any elemental crystalline silicon from their processingor the formation of graphene sheets. The Kaneda patent describes theembedding of the SiO particles within graphite particles, and theydescribe very high surface areas consistent with highly porousmaterials. The formation of small amounts of crystalline silicon fromthe HEMM of SiO was described in published U.S. patent application2012/0295155 to Deng et al. (hereinafter the Deng application), entitled“Silicon Oxide Based High Capacity Anode Materials for Lithium IonBatteries,” incorporated herein by reference. The Deng application alsodescribes the milling of SiO with graphite, and similar to the resultsin the Kaneda patent, the results in the Deng application do notdemonstrate any crystalline silicon formation from the milling withgraphite. The materials described herein have within the resultingcomposite material processed silicon suboxide, which may or may notresult significant quantities of crystalline silicon observable by x-raydiffraction.

Graphene sheets are thin layers of graphitic carbon. Essentially, thesheets have an extended array of hexagonal aromatic carbon rings andhave good electrical conductivity along the pane and high mechanicalstrength. There is relatively weak bonding between the planes of carbonin graphite, so the sheets are susceptible to exfoliation, i.e.,shearing to separate the layers from each other. Graphene sheetsformally may refer to a single carbon layer, which can be somewhatunstable in isolated form with respect to curving and otherdeformations. For the purposes herein, a sheet with a few atomic layersof graphitic carbon may accomplish similar properties of stabilizationof the silicon materials, so that a rigid reference to an ideal graphenesheet is not particularly relevant. For example, two layers of graphiticcarbon may not be distinguishable easily in micrographs from a singlelayer. However, the graphitic x-ray diffraction peaks are observed to goaway with the observation in TEM micrographs if graphene sheets areformed in the milling. Examination of TEM micrographs can be difficultto interpret in terms of evaluating thickness of graphitic sheets, butthe disappearance of the x-ray scattering peaks are consistent withgraphene sheets to be 1 or a few layers. For the purposes herein,graphene sheet is used to refer to graphitic carbon having a thicknessfrom 1 to 7 layers that do not diffract x-rays with a graphitic carbonpeak, which is formed from stacked graphitic carbon layers. In thecomposite materials, the graphitic carbon may be in a distribution ofthicknesses. Under the reasonable balancing of processing conditionsdescribed herein, generally a significant fraction but not all of thegraphite is converted to graphene sheets, as demonstrated by a reductionin the graphite x-ray scattering peak.

The mechanical processing, which may include chemical reduction, ofsilicon suboxide can form a high capacity material, such as nanoscalecrystalline silicon in nano-particles and/or in nanoscale domains ormultidomain particles, but as described below the precise nature of thematerial may not be clear. The exfoliated graphene sheets can form anelectrically conductive matrix that is believed to facilitate structuralaccommodation of the volume changes associated with lithium uptake andrelease from silicon and silicon suboxides. A range of useful compositematerials can be formed, and the design of the composite can becharacterized with respect to balance with respect to the nature of thecomposite constituent, and the control of the milling process to achievethe balance of composite composition is described further below.

The product material can be described in terms of the surface area,visible morphology in micrographs, elemental analysis by energydispersive X-ray spectroscopy in conjunction with transmission electronmicroscopy, and x-ray diffraction. However, as noted above, certaincharacteristics of the material cannot be directly measured. Therefore,the electrochemical characterization can provide valuable information onthe compositions in conjunction with other characterization tools. Inthe first milling step, the product material can be characterized by asurface area, average particle size and the identification ofcrystalline silicon identifiable from x-ray diffraction. In general, asurface area can be at least about 2.5 m²/g and the average secondaryparticle size (D50) can be no more than about 4 microns. With respect tosilicon x-ray peaks, good battery results have been obtained with noidentifiable Si scattering peak and with sizeable crystalline Siscattering peaks. There can be a balance of capacity versus cyclingstability, and further stabilization of the materials in the future caninfluence the selected balance of the material properties. In any case,it is believed that modification of the starting silicon suboxide issignificant regardless of whether or not crystalline x-ray diffractionpeaks are visible, so ending milling with a degree of modification,which may or may not involve overall chemical reduction, somewhat shortof producing crystalline Si scattering peaks is observed to produce aproduct material that has comparable reversible specific capacity cycledagainst lithium metal as samples with strong crystalline Si x-rayscattering peaks.

Upon incorporation into a composite material, the graphene/graphitematerials can be effective to stabilize the composite material withrespect to electrochemical cycling with incorporation and release oflithium at relatively low concentrations. The carbon component addsweight with at most a small contribution to the capacity. In general,the composite material comprises from about 0.5 weight percent to about20 weight percent graphitic carbon, e.g., graphite and/or graphene. Asnoted below, the oxidation state of the processed silicon suboxide mayor may not be well known, but the material nevertheless is wellcharacterized overall. The second milling step results in a materialwith a significant increased surface area that is believed to beassociated with exfoliation of the graphite into graphene sheets, andthe surface area generally is at least about 12 m²/g. Average secondaryparticle size measurements generally decrease with additional millingand can be generally from about 5 microns to 500 nanometers.

Two sequential milling steps can be performed to synthesize a desirableprocessed silicon suboxide-graphitic carbon composites. During the firstmilling step, silicon suboxide is chemically altered, although it is notknown if the material overall is reduced or if the microscopic domainstructure becomes segregated into more active elemental silicon domainswhile other domains become more oxidized. If sufficient processing,generally through high energy mechanical milling, is performed,crystalline silicon x-ray diffraction can be observed, but lesserdegrees of processing can be sufficient to obtain desired degrees oflithium intercalation/alloying capacity. Improved milling of siliconsuboxide described herein provides for the in situ synthesis ofprocessed silicon oxide with little or no contamination from the millingmedium, e.g., zirconia, to generate a high capacity material. Whilesignificant amounts of small silicon crystallites can be formed in acomposite material with the processed silicon suboxide, the degree ofprocessing of the silicon suboxide can be tuned to yield desirableproperties. In particular, while processing can increase the amount ofcrystalline nanoscale elemental silicon, improved cycling may resultfrom more mild processing of the silicon suboxide. The surface areaincreases from the milling.

While the growth of x-ray diffraction peaks corresponding to crystallinesilicon can both confirm the modification of silicon suboxide as well asprovide information on the degree of modification, an extrapolation ofthe processing conditions and the observation of consistentelectrochemical performance make it clear that significant modificationof silicon suboxide takes place even if crystalline silicon x-raydiffraction is not observed. If no crystalline silicon is directlyobserved, the electrochemical data in view of the processing is areasonable way to consider the degree of the modification of the siliconsuboxide as a result of the processing. Under conditions for themodification of silicon suboxide without observable crystalline siliconpeaks, it is not known if the processing forms small domains of eithercrystalline or amorphous Si that are too small to defract x-rays. Tocover the range of compositions resulting from the processing of siliconsuboxide, the material is referred to herein as processed siliconsuboxide, whether or not visible crystalline Si x-ray scattering peaksare observed. The milling also reduces the overall particulate size andcorrespondingly increases the surface area. The processed siliconsuboxide imparts a significant specific capacity with respect to lithiumuptake and release for the product material. Improvements in the millingof silicon suboxide provide for greater modification of the siliconsuboxide with reduced contamination of the milling media in comparisonwith results presented by the Deng application cited above.

During the second milling step, milling of the processed siliconsuboxide material with graphite forms graphene sheets that provide adesirable degree of stabilization of the resulting ultimate compositematerial. In particular, particles of processed silicon suboxide areembedded between graphene sheets as a result of the high energy millingprocess. The degree of exfoliation of the graphic can be controlledduring processing conditions. An intermediate degree of processing hasbeen found to result in a composite with significantly greaterstability. Overall, the two step processing is found to producecomposite materials that have not been achieved with single stepprocessing suggesting that the environment during the high energymilling significantly influences the chemical and structuraltransformations that occur within the complex composite material.

It has been discovered that balance with respect to both milling stepscan be effective to obtain particularly desirable materials, although arange of product composite materials can yield very good electrochemicalproperties. With respect to the first milling step, the degree ofprocessing of the silicon suboxide, which may or may not results inidentifiable crystalline silicon, can be controlled based on the x-raydiffraction spectrum or extrapolation under milder milling conditionsand/or a study of the electrochemical properties of the productmaterial. While it may seem desirable to increase the amount of in situnanoscale elemental silicon from a capacity perspective, high capacitiescan be obtained with milder processing of the silicon suboxide, and goodcycling can similarly be obtained with the milder processing of siliconsuboxide. Thus, the selection of the amount of crystalline nanoscalesilicon can be adjusted with these issues to guide the processingdesign. While the product processed silicon suboxide-graphitic carboncomposite can have a prominent crystalline silicon x-ray scatteringpeak, such a prominent peak may or may not be observed for somedesirable battery materials. Also, the second milling step similarly caninvolve balance. Although increased milling of the blend comprisinggraphite is observed to increase exfoliation of the graphite intographene, excessive milling seems to adversely influence the siliconbased active phases of the materials. Similarly, while formation ofgraphene sheets seem desirable for stabilization based on the dataherein, it is not currently clear whether or not maintenance of somegraphite itself is or is not desirable.

The processed silicon suboxide-graphitic carbon composites comprise aselected relative amount of silicon and graphitic carbon with acorresponding amount of processing to provide compositions with desiredproperties. The relative amounts of silicon and graphite are determinedby the starting materials for the second milling step. In general, arelatively low amount of graphitic carbon can be included in thecomposite to provide the electrochemical stabilization. Theelectrochemical capacity generally is determined primarily by thesilicon component of the material. The processing conditions can be usedindependently to control the degree of silicon suboxide modification andthe degree of graphite exfoliation. Processing parameters also controlthe surface area and particle size of the product material. The productmaterial exhibits excellent cycling at a relatively high specificcapacity.

In general, the milling process can comprise an approach that providesdesired milling forces to modify silicon oxide in the first processingstep and exfoliate graphite in the second processing step, such as jarmilling and/or ball milling, such as planetary ball milling. Ballmilling and similarly jar milling can involve grinding using a grindingmedium, which can then be substantially removed from the groundmaterial. A planetary ball mill is a type of ball milling in which themill comprises a sun-wheel, at least one grinding jar mountedeccentrically on the sun-wheel, and a plurality of mixing balls withinthe grinding jar. In operation, the grinding jar rotates about its ownaxis and in the opposite direction around the common axis of thesun-wheel. The milling settings can be selected based on the particularmilling configuration, such as the size of the milling jar and millingmedium, which have been found to influence the forces delivered to theprocessing compositions. Also, suitable milling may be wet milling ordry milling. As noted above, the design of the product material caninvolve a balance of considerations, and correspondingly, the millingcan involve a corresponding balance and generally not application of thegreatest amount of milling force for the longest amount of time.

Battery Structure

In general, the lithium ion battery described herein comprises apositive electrode comprising a lithium intercalation material and anegative electrode comprising a lithium intercalation/alloying material,such as the processed silicon suboxide-graphitic carbon compositesdescribed herein. The nature of the positive electrode active materialand the negative electrode active material influences the resultingvoltage of the battery since the voltage is the difference between thehalf cell potentials at the cathode and anode. As described in detailbelow with respect to specific battery designs, the batteries generallyhave a positive electrode or cathode, a negative electrode or anode witha separator layer between the positive electrode and negative electrode,separate current collectors associated with the respective electrodes,electrolyte for ion mobility and a container. For larger capacitysecondary batteries, an electrode stack with a plurality of electrodesof each polarity are generally assembled in a stack.

Suitable positive electrode active materials are described below, andthe materials of particular interest are lithium metal oxides.Generally, suitable negative electrode lithium intercalation/alloyingcompositions can include, for example, graphite, synthetic graphite,coke, fullerenes, other graphitic carbons, niobium pentoxide, tinalloys, silicon, silicon alloys, silicon-based composites, titaniumoxide, tin oxide, and lithium titanium oxide, such as Li_(x)TiO₂,0.5≤x≤1 or Li_(1+x)Ti_(2−x)O₄, 0≤x≤⅓. However, as described herein,improved negative electrode active materials generally comprise highcapacity silicon-based materials, which can comprise processed siliconsuboxide-graphitic carbon composite material. Silicon based activematerials take up lithium to form an alloy and release lithium from thealloy to correspondingly release lithium, and have a relatively lowpotential relative to lithium such that they can be substituted forlithium without dramatic changes in voltage of the resulting battery incomparison with a corresponding battery with a lithium metal negativeelectrode. Negative electrode active materials of particular interestare described in detail below.

The positive electrode active compositions and negative electrode activecompositions generally are powder compositions that are held together inthe respective electrode with a polymer binder. The binder allows forionic conductivity to the active particles when in contact with theelectrolyte. Suitable polymer binders include, for example,polyvinylidine fluoride (PVDF), polyethylene oxide, polyimide,polyethylene, polypropylene, polytetrafluoroethylene, polyacrylates,rubbers, e.g. ethylene-propylene-diene monomer (EPDM) rubber or styrenebutadiene rubber (SBR), copolymers thereof, or mixtures thereof. Inparticular, thermally curable polyimide polymers have been founddesirable for high capacity silicon-based electrodes, which may be dueto their high mechanical strength. The following Table 1 providessuppliers of polyimide polymers, and names of corresponding polyimidepolymers.

TABLE 1 Supplier Binder New Japan Chemical Co., Ltd. Rikacoat PN-20;Rikacoat EN-20; Rikacoat SN-20 HD MicroSystems PI-2525; PI-2555;PI-2556; PI-2574 AZ Electronic Materials PBI MRS0810H Ube Industries.Ltd. U-Varnish S; U-Varnish A Maruzen petrochemical Co., Ltd. Bani-X(Bis-allyl-nadi-imide) Toyobo Co., Ltd. Vyromax HR16NN

With respect to polymer properties, some significant properties forelectrode application are summarized in the following Table 2.

TABLE 2 Tensile Elastic Viscosity Binder Elongation Strength (MPa)Modulus (P) PVDF  5-20% 31-43 160000 psi 10-40 Polyimide 70-100% 150-30040-60 CMC  30-40% 10-15 30

PVDF refers to polyvinylidene fluoride, and CMC refers to sodium carboxymethyl cellulose. The elongation refers to the percent elongation priorto tearing of the polymer. In general, to accommodate the silicon basedmaterials, it is desirable to have an elongation of at least about 50%and in further embodiments at least about 70%. Similarly, it isdesirable for the polymer binder to have a tensile strength of at leastabout 100 MPa and in further embodiments at least about 150 MPa. Tensilestrengths can be measured according to procedures in ASTM D638-10Standard Test Method for Tensile Properties of Plastics, incorporatedherein by reference. A person of ordinary skill in the art willrecognize that additional ranges of polymer properties within theexplicit ranges above are contemplated and are within the presentdisclosure. The particle loading in the binder can be large, such asgreater than about 80 weight percent. To form the electrode, the powderscan be blended with the polymer in a suitable liquid, such as a solventfor the polymer. The resulting paste can be pressed into the electrodestructure.

The active particle loading in the binder can be large, such as greaterthan about 80 weight percent, in further embodiments at least about 83weight percent and in other embodiments from about 85 to about 97 weightpercent active material. A person of ordinary skill in the art willrecognize that additional ranges of particles loadings within theexplicit ranges above are contemplated and are within the presentdisclosure. To form the electrode, the powders can be blended with thepolymer binder in a suitable liquid, such as a solvent for the polymerbinder. The resulting paste can be pressed into the electrode structure.

The positive electrode composition, and in some embodiments the negativeelectrode composition, generally can also comprise an electricallyconductive powder distinct from the electroactive composition. Suitablesupplemental electrically conductive powders include, for example,graphite, carbon black, metal powders, such as silver powders, metalfibers, such as stainless steel fibers, and the like, and combinationsthereof. Generally, an electrode can comprise from about 1 weightpercent to about 25 weight percent, and in further embodiments fromabout 2 weight percent to about 20 weight percent and in otherembodiments from about 3 weight percent to about 15 weight percentdistinct electrically conductive powder. A person of ordinary skill inthe art will recognize that additional ranges of amounts of electricallyconductive powders within the explicit ranges above are contemplated andare within the present disclosure. Specific electrically conductivematerials for high capacity negative electrodes are described furtherbelow.

Each electrode generally is associated with an electrically conductivecurrent collector to facilitate the flow of electrons between theelectrode and an exterior circuit. A current collector can comprise ametal structure, such as a metal foil or a metal grid. In someembodiments, a current collector can be formed from nickel, aluminum,stainless steel, copper or the like. An electrode material can be castas a thin film onto a current collector. The electrode material with thecurrent collector can then be dried, for example in an oven, to removesolvent from the electrode. In some embodiments, a dried electrodematerial in contact with a current collector foil or other structure canbe subjected to a pressure from about 2 to about 10 kg/cm² (kilogramsper square centimeter).

The separator is located between the positive electrode and the negativeelectrode. The separator is electrically insulating while providing forat least selected ion conduction between the two electrodes. A varietyof materials can be used as separators. Commercial separator materialscan be formed from polymers, such as polyethylene and/or polypropylenethat are porous sheets that provide for ionic conduction. Commercialpolymer separators include, for example, the Celgard® line of separatormaterial from Hoechst Celanese, Charlotte, N.C. Suitable separatormaterials include, for example, 12 micron to 40 micron thick trilayerpolypropylene-polyethylene-polypropylene sheets, such as Celgard® M824,which has a thickness of 12 microns. Also, ceramic-polymer compositematerials have been developed for separator applications. Thesecomposite separators can be stable at higher temperatures, and thecomposite materials can significantly reduce the fire risk.Polymer-ceramic composites for lithium ion battery separators are soldunder the trademark Separion® by Evonik Industries, Germany.

The electrolyte provides for ion transport between the anode and cathodeof the battery during the charge and discharge processes. We refer tosolutions comprising solvated ions as electrolytes, and ioniccompositions that dissolve to form solvated ions in appropriate liquidsare referred to as electrolyte salts. At least some of the irreversiblecapacity loss can be attributed to the formation of a solventelectrolyte interphase layer associated with the electrodes, and inparticular with the negative electrode. Electrolytes for lithium ionbatteries can comprise one or more selected lithium salts. Suitablelithium salts include, for example, lithium hexafluorophosphate, lithiumhexafluoroarsenate, lithium bis(trifluoromethyl sulfonyl imide), lithiumtrifluoromethane sulfonate, lithium tris(trifluoromethyl sulfonyl)methide, lithium tetrafluoroborate, lithium perchlorate, lithiumtetrachloroaluminate, lithium chloride, lithium difluoro oxalato borate,and combinations thereof. Traditionally, the electrolyte comprises a 1 Mconcentration of the lithium salts, although greater or lesserconcentrations can be used.

For lithium ion batteries of interest, a non-aqueous liquid is generallyused to dissolve the lithium salt(s). The solvent generally does notdissolve the electroactive materials. Appropriate solvents include, forexample, propylene carbonate, dimethyl carbonate, diethyl carbonate,2-methyl tetrahydrofuran, dioxolane, tetrahydrofuran, methyl ethylcarbonate, γ-butyrolactone, dimethyl sulfoxide, acetonitrile, formamide,dimethyl formamide, triglyme (tri(ethylene glycol) dimethyl ether),diglyme (diethylene glycol dimethyl ether), DME (glyme or1,2-dimethyloxyethane or ethylene glycol dimethyl ether), nitromethaneand mixtures thereof. Particularly useful solvents for high voltagelithium-ion batteries are described further in published U.S. patentapplications 2011/0136019 to Amiruddin et al. entitled: “Lithium ionbattery with high voltage electrolytes and additives”, incorporatedherein by reference.

The porous silicon based material described herein can be incorporatedinto various commercial battery designs such as prismatic shapedbatteries, wound cylindrical batteries, coin cell batteries, or otherreasonable battery shapes. The batteries can comprise a single pair ofelectrodes or a plurality of pairs of electrodes assembled in paralleland/or series electrical connection(s). While the materials describedherein can be used in batteries for primary, or single charge use, theresulting batteries generally have desirable cycling properties forsecondary battery use over multiple cycling of the batteries.

In some embodiments, the positive electrode and negative electrode canbe stacked with the separator between them, and the resulting stackedstructure can be rolled into a cylindrical or prismatic configuration toform the battery structure. Appropriate electrically conductive tabs canbe welded or the like to the current collectors and the resultingjellyroll structure can be placed into a metal canister or polymerpackage, with the negative tab and positive tab welded to appropriateexternal contacts. Electrolyte is added to the canister, and thecanister is sealed to complete the battery. Some presently usedrechargeable commercial batteries include, for example, the cylindrical18650 batteries (18 mm in diameter and 65 mm long) and 26700 batteries(26 mm in diameter and 70 mm long), although other battery sizes can beused, as well as prismatic cells and foil pouch batteries of selectedsizes.

Pouch cell batteries can be particularly desirable for vehicleapplications due to stacking convenience and relatively low containerweight. A representative embodiment of a pouch battery is shown in FIG.1A-1D. Specifically, pouch cell battery 100 as shown in FIG. 1A as agenerally approximate rectangular parallelepiped, excluding theconnection tabs and other potential features around the edges,characterized by a thickness (t) and a planar area with a width (w) anda height (h) in which the thickness is generally significantly less thanthe linear dimensions (width and height) defining the planar area (w·h).The pouch enclosure 102, battery core 104 and pouch cover 106 of thebattery 100 is taken apart and illustrated in FIG. 1B. As shown in FIG.1 {b), terminal tabs 114, 116 extend outward from the battery core 104.Pouch enclosure 102 comprises a cavity 110 and edge 112 surrounding thecavity. Cavity 110 has dimensions such that battery core 104 can fitwithin cavity 110. Pouch cover 106 can seal around edge 112 to sealbattery core 104 within the cavity 110 to form the sealed battery 100.FIG. 1C is an illustration of a perspective view of the sealed battery100 with the pouch cover 106 at the bottom and the cavity 110 showing asprotrusion from the pouch cover 106. Terminal tabs 114, 116 are shownextending outward from the sealed pouch for electrical contact. FIG. 1Dis a schematic diagram of a cross section of the battery 100 viewedalong the d-d line of FIG. 1C. Specifically, battery core 104 is shownto be encased inside the cavity 110 of the pouch enclosure 102 sealedalong the edge 112 with pouch cover 106. Many additional embodiments ofpouch batteries are possible with different configurations of the edgesand seals. However, reasonable configurations of the pouch batteries cantake advantage of the desired design parameters described herein.

In the embodiments of particular interest herein, the electrodes arestacked in battery core 104 with a stack of positive electrodes 124(cathodes) and negative electrodes 122 (anodes) with a sheet ofseparator 126 between adjacent electrodes of opposite parity, as shownin FIG. 1E. For secondary batteries designed to operate at reasonablerates for most applications, it has been found that the electrodesperform appropriately if they are not too thick, and anode loadinglevels are explored in the examples. Appropriate electrically conductivetabs can be welded or the like to the current collectors to form currentcollector tabs. Referring to FIG. 1E, electrically conductive tabs 134are electrically connected with positive electrodes 124 and electricallyconductive tabs 128 are electrically connected with negative electrodes126. Generally, the electrode plates in the stack of like polarity areconnected in parallel. In other words, current collector tabs of thepositive electrodes are connected, e.g., welded or the like, to a commonelectrical conductive element, and the current collector tabs of thenegative electrodes are connected to a common electrical conductiveelement. Referring to FIG. 1E, current collector 136 is electricallyconnected with electrically conductive tabs 134 and currently collector130 is electrically connected with electrically conductive tabs 128.Current collectors 130,136 are respectively terminated with negativeterminal tab 114 and positive terminal tab 116. Suitable electricallyconductive elements include, for example, a metal strip, wire or thelike. With a parallel connection, the capacity of the battery is the sumof the capacities available from the individual electrodes. The batterycore can be placed into the pouch, with the negative terminal tab 114and the positive terminal tab 116 extending from the pouch packagingmaterial to provide connection to appropriate external contacts, asindicated in FIG. 1E. Electrolyte is added to the pouch, and the pouchis sealed to complete the battery.

A desirable pouch battery design for vehicle batteries incorporating ahigh capacity cathode active materials is described in detail inpublished U.S. patent applications 2009/0263707 to Buckley et al,entitled “High Energy Lithium Ion Secondary Batteries,” incorporatedherein by reference. Specific designs for batteries for vehicle useincorporating high capacity positive electrode active material andnegative electrode active material are described in detail in copendingU.S. patent application Ser. No. 13/777,722 to Masarapu et al., now U.S.Pat. No. 9,780,358, entitled “Battery Designs With High Capacity AnodeMaterials and Cathode Materials,” and copending U.S. patent applicationSer. No. 13/464,034 to Masarapu et al. (the '672 application), now U.S.Pat. No. 10,553,871, entitled “Battery Cell Engineering and Design toReach High Energy,” both incorporated herein by reference.

Composite Silicon Based Active Materials and Processing to Form theMaterials

Composite materials comprise processed silicon suboxide to provide ahigh specific capacity and graphitic carbon with a graphene component tostabilize the silicon based material as well as increase electricalconductivity. The silicon suboxide component of the composite may or maynot comprise measurable crystalline silicon. Two high energy millingsteps can be used to form the desired composite compositions. In thefirst milling step, mechanical forces from the milling induce themodification of a silicon suboxide starting material. In the secondmilling step, the product of the first milling step is milled with apowder of graphite which results in the exfoliation of at least aportion of the graphite to form graphene. The graphene formation seemsto be associated with significant stabilization of the resulting activematerial when cycled in a lithium based battery.

The relative amounts of processed silicon suboxide and graphitic carboncan be balanced to achieve desired levels of specific capacity andstability. In general, commercial battery grade graphite powder can beused as the graphite component added for the second high energymechanical milling step. In general, natural graphite, syntheticgraphite or a combination thereof can be used. The relative amounts ofprocessed silicon suboxide and graphitic carbon are determined by thematerials added into the second milling step, and it is assumed for thepurpose of evaluating relative amounts of components that the masses ofthe components do not change as a result of the high energy mechanicalmilling process even though the form of the graphitic carbon changes. Ingeneral, a relatively low amount of graphitic carbon can be used toachieved desired results, and a corresponding relatively largeproportion of silicon based active material can contribute to acorrespondingly large specific capacity.

To the extent that a modest addition of silicon based active materialcan increase the capacity of the composite material, the composite caneffectively comprise a wide range of graphite to form a desirablecomposite material. Thus, the composite material can comprise from about0.5 weight percent graphitic carbon to about 95 weight percent graphiticcarbon, in further embodiments from about 4 weight percent to about 90weight percent, and in other embodiments from about 8 weight percentgraphitic carbon to about 85 weight percent. In some embodiments, it isdesirable to have a high specific capacity material with a more modestamount of graphite, so it is useful to consider ranges of compositionaccordingly in which the composite comprises. For some embodiments, thecomposite material can comprise from about 0.5 weight percent graphiticcarbon to about 30 weight percent graphitic carbon, in furtherembodiments from about 1 weight percent to about 25 weight percent, inother embodiments from about 3 weight percent graphitic carbon to about20 weight percent, and in additional embodiments from about 4 weightpercent to about 15 weight percent graphitic carbon. A person ofordinary skill in the art will recognize that additional ranges ofgraphitic carbon concentrations within the explicit ranges above arecontemplated and are within the present disclosure.

In some contexts, the term graphene has been used to refer to an idealsingle layer of graphitic, i.e., an aromatic sheet, of carbon. In morecommercial application contexts, graphene generally refers to exfoliatedgraphite generally with no more than about 7 layers, i.e., 1-7 layers,of graphitic carbon and possibly including a distribution of layerthicknesses as well as varying layer thickness across a particularsheet. It can be difficult to evaluate the thicknesses of graphenesheets in the context of a composite material, as in the present case.However, the graphene sheets can be observed in micrographs as thinstructures, and the magnitude of the graphite x-ray diffraction peak isobserved to diminish consistent with observations in micrographs of theexfoliation process. The degree of disappearance of the graphite x-raydiffraction peak can provide a measure of the degree of graphiteexfoliation. The exfoliation of the graphite into graphene sheets alsoseems to be correlated with an increase in surface area of the productmaterial, which is believed to be generally consistent with theformation of graphene sheets with a plurality of carbon layers since thesurface area increases are significant but not large.

In some embodiments, composite materials with good stability and highdischarge capacities are observed to have significant fractions of thegraphite converted to graphene but with significant amounts of remaininggraphite based on x-ray diffraction. With composite samples obtained inthe Examples, the electrochemical capacity of the material decreasedsignificantly with further high energy mechanical milling to exfoliatethe graphite, but prior to conversion of all of the graphite tographene, as evaluated by observation of the graphite x-ray diffraction.According to the data in the Examples below, the qualitative trend inthe data indicates that significant graphene formation is associatedwith an increase in capacity and stabilization with cycling but thatexcessive exfoliation of graphene is associated with a drop in capacityand stabilization.

High energy mechanical milling can generally reduce the averagesecondary particle sizes. Secondary particles size refers to theparticle size in a dispersion, and the secondary particle size can bemeasured by dynamic light scattering or the like. For convenience,volume average particle sizes are reported as D₅₀ values. Directmeasurements by dynamic light scattering (DLS) are intensity weightedparticle size distributions, and these can be converted to volume baseddistributions using conventional techniques. The volume-average particlesize can be evaluated from the volume-based particle size distribution.Suitable particle size analyzers include, for example, a Microtrac UPAinstrument from Honeywell and Saturn DigiSizer™ from Micromeritics basedon dynamic light scattering, a Horiba Particle Size Analyzer fromHoriba, Japan and ZetaSizer Series of instruments from Malvern based onPhoton Correlation Spectroscopy. The principles of dynamic lightscattering for particle size measurements in liquids are wellestablished.

The formation of the composite through the exfoliation of the graphiteincreases the surface area of the material. In some embodiments, theprocessed silicon suboxide-graphitic carbon composite has a BET surfacearea from about 12 m²/g to about 35 m²/g, in further embodiments fromabout 14 m²/g to about 33 m²/g and in further embodiments from about 15m²/g to about 32 m²/g. BET surface area can be measured using gasadsorption, for example, as measured with commercially availableequipment, and Standards are available for basing these measurements,e.g., ASTM Standard C1274-12 “Standard Test Method for Advanced CeramicSpecific Surface Area by Physical Adsorption,” incorporated herein byreference. The processed silicon suboxide-graphitic carbon composite canhave a D50 volume average particle size of no more than about 10microns, in further embodiments from about 0.75 microns to about 9microns and in additional embodiments from about 0.8 microns to about 8microns. A person if ordinary skill in the art will recognize thatadditional ranges of BET surface area and D50 volume average secondaryparticle sizes within the explicit ranges above are contemplated and arewithin the present disclosure. The secondary particle size distributionsare observed to have a bimodal distribution.

The processed silicon suboxide material from the first high energymechanical milling step is a starting material for the second highenergy mechanical milling step, and the properties of the processedsilicon suboxide can influence the properties of the ultimate composite.In its broadest sense, silicon suboxide can be written with a formulaSiO_(x), 0≤x<2. As described in the Examples below, the startingmaterials for the synthesis were commercial powders of SiO. Whilemetastable SiO has been reported in the gas phase, the solid can take ona complex material structure that is not necessarily stoichiometric. SiOcan be formed with a high temperature reaction of Si and SiO₂. For useas an active material for a lithium ion battery, silicon suboxidegenerally refers to amorphous oxygen deficient silicon oxidesrepresented by formula SiO where 0.1≤x≤1.9, in further embodiments0.15≤x≤1.8, in other embodiments 0.2≤x≤1.6 and in additional embodiments0.25≤x≤1.5. In some embodiments, x≈1 and the silicon oxide isrepresented approximately by formula SiO. A person of ordinary skill inthe art will recognize that additional ranges of silicon oxidestoichiometry within the explicit ranges above are contemplated and arewithin the present disclosure.

In some embodiments, peaks corresponding to crystalline silicon can beobserved with respect to the processed silicon suboxide material, butunder lesser processing conditions a desirable level of specificcapacity can be observed without necessarily seeing a visible x-raydiffraction peak corresponding to elemental silicon. Based on anextrapolation of the observations, it seems that a degree ofmodification of the material is taking place whether or not x-raydiffraction provides an evidence of elemental silicon generation. Whilethe observation of crystalline silicon x-ray scattering peaks canprovide direct evidence of material modification of the siliconsuboxide, the observed degrees of specific capacity is essentially alsodiagnostic for the modification of the silicon, although lessinformation is provided regarding the phase structure of the siliconmaterial, which may likely be complex whether or not elemental silicondomains are manifested. Nevertheless, under appropriate processingconditions it seems fair to conclude that modification of the siliconsuboxide takes place, and the HEMM milled materials are correspondinglyreferred to as processed silicon suboxides.

While the formation of elemental silicon may increase the specificcapacity, larger quantities of elemental silicon can result in decreasedcycling stability for the materials. Some elemental silicon was observedfrom processing of silicon suboxide in the Deng application cited above.In order to achieve desired degrees of cycling stability at a relativelyhigh specific capacity, the degree of modification of the siliconsuboxide through the milling process can be balanced to provide adesired performance of the materials. Generally, the processed siliconsuboxide also has an increased surface area. In some embodiments, theBET surface area can be at least about 2 m²/g, in further embodimentsfrom about 2.5 m²/g to about 20 m²/g and in additional embodiments fromabout 3 m²/g to about 17 m²/g. A person of ordinary skill in the artwill recognize that additional ranges of surface area within theexplicit ranges above are contemplated and are within the presentdisclosure.

The milling also decreases the average particle size of the processedsilicon suboxide. The secondary particle size can be measured by dynamiclight scattering of a dispersion in a suitable liquid. The volume basedD50 values can be no more than about 10 microns and in furtherembodiments from about 0.3 microns to about 9 microns. A person ofordinary skill in the art will recognize that additional ranges of D50values within the explicit ranges above are contemplated and are withinthe present disclosure.

The high energy mechanical milling generally involves jar milling and/orball milling with a suitable mill, such as a planetary ball mill. Ballmilling and similarly jar milling may involve grinding using a grindingmedium, such as ceramic particles, which can then be substantiallyremoved from the ground material. A planetary ball mill is a type ofball milling in which the mill comprises a sun-wheel, at least onegrinding jar mounted eccentrically on the sun-wheel, and a plurality ofmixing balls within the grinding jar. In operation, the grinding jarrotates about its own axis and in the opposite direction around thecommon axis of the sun-wheel. High energy mechanical milling can providemechanical forces to induce significant structural changes to the milledmaterial.

The high energy mechanical milling can be performed by dry milling withonly particles of grinding media or wet milling with a liquid inaddition to the particles of grinding media. Suitable liquids caninclude aqueous solvents, organic solvents, such as alcohols, ormixtures thereof. Ethanol, isopropanol or other low molecular weightalcohols can be convenient liquid media. The mill container can befilled with an inert gas, such as nitrogen or argon, to avoid oxidizingthe contents of the container during milling. Examples of suitablegrinding media include, for example, particles of zirconia, alumina,tungsten carbide, other dense ceramic compositions or the like. Themilling media is generally chosen to be harder and denser than thematerials being milled, and milling conditions and be selected toachieve little if any milling media contamination in the productmaterial. The selection of the amount of milling media and size ofmilling balls can be selected to balance the energy of the millingprocess based on observed physical changes to the material.

Desirable ball milling rotation rates and ball milling times can beselected based on the desired composition and structure of the productmaterials. For the formation of processed silicon suboxide andcorresponding composites with graphitic carbon, ball milling rotationrates generally can be from about 50 rpm to about 1000 rpm and infurther embodiments from about 75 rpm to about 700 rpm. Furthermore,desirable ball milling times can be from about 10 minutes to about 20hour and in further embodiments from about 20 minutes to about 10 hours.The weight ratio of milling media to material being milled is generallyfrom about 1:1 to about 25:1 and in further embodiments from about 1.5:1to about 15:1. A person of ordinary skill in the art will recognize thatadditional ranges of milling rates and times within the explicit rangesabove are contemplated and are within the present disclosure. Ingeneral, the milling media particle sizes are much larger than theparticle sizes of the material being milled, which allows for separationof the milling balls.

As noted above, the high energy milling to obtain the desired compositematerials is performed in two steps, which leads to desired compositionswith good electrochemical properties. In addition, each of the twomilling steps is balanced to provide a composition with desirableperformance properties. The first processing step is adjusted to providethe desired degree of silicon suboxide compositional modification aswell as reduction of particle size and increase in surface area. Whileadditional high energy mechanical milling of the silicon suboxide seemsto increase the modification of the material to form nanoscale elementalsilicon, the increased milling may adversely influence the cyclingstability of the material.

For the second high energy milling step to form the composite material,the processed silicon suboxide is combined with powdered graphite. Inthe second milling step, the degree of graphite exfoliation, decrease inparticle size and increase in surface area is balanced to provide acomposite material with a high specific capacity and desired cyclingstability. The graphite can be exfoliated during the second milling stepto form graphene sheets. The exfoliation of the graphite can be trackedby the diminishment of the x-ray scattering associated with graphite andthe observation of the appearance of graphene sheets in electronmicrographs. Correspondingly, the surface area of the materialincreases, and the average secondary particle size decreases. Relativeamounts of graphitic carbon and silicon based material can be balancedwith too low quantities of graphitic carbon not improving stabilitysufficiently, but greater amounts of graphitic carbon may not furtherimprove stability but may decrease specific capacity. Similarly,exfoliation of the graphite to form graphene stabilized the material upto a point, and evidence suggests that excessive exfoliation of thegraphite does not further improve the stability and may decreasecapacity and stability, perhaps due to damage of the structure of thesilicon based active material. Again, appropriate balance of theprocessing conditions results in a desirable product composite material.

High Capacity Positive Electrode Active Materials

In general, positive electrode (cathode) active materials comprise alithium intercalation material such as lithium metal oxides or lithiummetal phosphates. Positive electrode active materials include, forexample, as stoichiometric layered cathode materials with hexagonallattice settings like LiCoO₂, LiNiO₂, LiCo_(1/3)Mn_(1/3)Ni_(1/3)O₂ orthe like; cubic spinel cathode materials such as LiMn₂O₄, Li₄Mn₅O₁₂, orthe like; olivine materials, such as LiMPO₄ (M=Fe, Co, Mn, combinationsthereof and the like). Lithium rich positive electrode active materialsare of interest due to their high capacity, such as layered cathodematerials, e.g., Li_(1+x)(NiCoMn)_(0.33−x)O₂ (0≤x<0.3) systems;layered-layered composites, e.g., xLi₂MnO₃.(1−x)LiMO₂ where M can be Ni,Co, Mn, combinations thereof and the like; and composite structures likelayered-spinel structures such as LiMn₂O₄.LiMO₂. In some embodiments, alithium rich composition can be referenced relative to a compositionLiMO₂, where M is one or more metals with an average oxidation state of+3.

In some embodiments, the lithium rich compositions can be representedapproximately with a formula Li_(1+x)M_(1−y)O₂, where M represents oneor more non-lithium metals and y is related to x based on the averagevalance of the metals. In layered-layered composite compositions, x isapproximately equal to y. The additional lithium in the initial cathodematerial can provide to some degree corresponding additional activelithium for cycling that can increase the battery capacity for a givenweight of cathode active material. In some embodiments, the additionallithium is accessed at higher voltages such that the initial chargetakes place at a higher voltage to access the additional capacity.

Lithium rich positive electrode active materials of particular interestare represented approximately by a formulaLi_(1+b)Ni_(α)Mn_(β)Co_(γ)A_(δ)O_(2−z)F_(z),  Formula Iwhere b ranges from about 0.05 to about 0.3, a ranges from about 0 toabout 0.4, β ranges from about 0.2 to about 0.65, γ ranges from 0 toabout 0.46, δ ranges from 0 to about 0.15 and z ranges from 0 to about0.2 with the proviso that both α and γ are not zero, and where A is ametal element different from Ni, Mn, Co, or a combination thereof.Element A and F (fluorine) are optional cation and anion dopants,respectively. Element A can be, for example Mg, Sr, Ba, Cd, Zn, Al, Ga,B, Zr, Ti, Ca, Ce, Y, Nb, Cr, Fe, V, Li or combinations thereof. Aperson of ordinary skill in the art will recognize that additionalranges of parameter values within the explicit compositional rangesabove are contemplated and are within the present disclosure.

To simplify the following discussion in this section, the optionaldopants are not discussed further except for under the context of thefollowing referenced applications. The use of a fluorine dopant inlithium rich metal oxides to achieve improved performance is describe inpublished U.S. patent application 2010/0086854 to Kumar et al., entitled“Fluorine Doped Lithium Rich Metal Oxide Positive Electrode BatteryMaterials With High Specific Capacity and Corresponding Batteries,”incorporated herein by reference. The specific performance propertiesobtained with +2 metal cation dopants, such as Mg⁺², are described incopending U.S. patent application Ser. No. 12/753,312 to Karthikeyan etal., now U.S. Pat. No. 8,741,484, entitled “Doped Positive ElectrodeActive Materials and Lithium Ion Secondary Batteries ConstructedTherefrom,” incorporated herein by reference.

The formulas presented herein for the positive electrode activematerials are based on the molar quantities of starting materials in thesynthesis, which can be accurately determined. With respect to themultiple metal cations, these are generally believed to bequantitatively incorporated into the final material with no knownsignificant pathway resulting in the loss of the metals from the productcompositions. Of course, many of the metals have multiple oxidationstates, which are related to their activity with respect to thebatteries. Due to the presence of the multiple oxidation states andmultiple metals, the precise stoichiometry with respect to oxygengenerally is only roughly estimated based on the crystal structure,electrochemical performance and proportions of reactant metals, as isconventional in the art. However, based on the crystal structure, theoverall stoichiometry with respect to the oxygen is reasonablyestimated. All of the protocols discussed in this paragraph and relatedissues herein are routine in the art and are the long establishedapproaches with respect to these issues in the field.

The stoichiometric selection for the compositions can be based on somepresumed relationships of the oxidation states of the metal ions in thecomposition. As an initial matter, if in Formula I above, b+α+β+γ+δ isapproximately equal to 1, then the composition can be correspondinglyapproximately represented by a two component notation as:xLi₂M′O₃.(1−x)LiMO₂  Formula IIwhere 0<x<1, M is one or more metal cations with an average valance of+3 with at least one cation being a Mn ion or a Ni ion and where M′ isone or more metal cations with an average valance of +4. It is believedthat the layered-layered composite crystal structure has a structurewith the excess lithium supporting the formation of an alternativecrystalline phase. For example, in some embodiments of lithium richmaterials, a Li₂MnO₃ material may be structurally integrated with eithera layered LiMO₂ component where M represents selected non-lithium metalelements or combinations thereof. These compositions are describedgenerally, for example, in U.S. Pat. No. 6,680,143 to Thackeray et al.,entitled “Lithium Metal Oxide Electrodes for Lithium Cells andBatteries,” which is incorporated herein by reference.

Recently, it has been found that the performance properties of thepositive electrode active materials can be engineered around thespecific design of the composition stoichiometry. The positive electrodeactive materials of particular interest can be represented approximatelyin two component notation as:xLi₂MnO₃.(1−x)LiMO₂  Formula IIIwhere M is one or more metal elements with an average valance of +3 andwith one of the metal elements being Mn and with another metal elementbeing Ni and/or Co. In general, in Formula II and III above, the x is inthe range of 0<x<1, but in some embodiments 0.03≤x≤0.6, in furtherembodiments 0.075≤x≤0.50, in additional embodiments 0.1≤x≤0.45, and inother embodiments 0.15≤x≤0.425. A person of ordinary skill in the artwill recognize that additional ranges within the explicit ranges ofparameter x above are contemplated and are within the presentdisclosure. In some embodiments, M in Formula III comprises manganese,nickel, cobalt or a combination thereof along with an optional dopantmetal and can be written as Ni_(u)Mn_(v)Co_(w)A_(y), where A is a metalother than Ni, Mn or Co. Consequently Formula III now becomes:x.Li₂MnO₃.(1−x)LiNi_(u)Mn_(v)Co_(w)A_(y)O₂  Formula IVwhere u+v+w+y≈1. While Mn, Co and Ni have multiple accessible oxidationstates, which directly relates to their use in the active material, inthese composite materials if appropriate amounts of these elements arepresent, it is thought that the elements can have the oxidation statesMn⁺⁴, Co⁺³ and Ni⁺². In the overall formula, the total amount ofmanganese has contributions from both constituents listed in the twocomponent notation.

In some embodiments, the stoichiometric selection of the metal elementscan be based on the above presumed oxidation states. Additionally, ifδ=0 in Formula I, the two component notation of Formula IV can simplifywith v≈u to x.Li₂MnO₃.(1−x)LiNi_(u)Mn_(u)Co_(w)O₂, with 2u+w=1. Also,compositions can be considered in which the composition varies aroundthe stoichiometry with v≈u. The engineering of the composition to obtaindesired battery performance properties is described further in U.S. Pat.No. 8,394,534 (the '534 patent) to Lopez et al., entitled “Layer-LayerLithium Rich Complex Metal Oxides With High Specific Capacity andExcellent Cycling,” incorporated herein by reference. Similarcompositions have been described in U.S. Pat. No. 8,389,160 (the '160patent) to Venkatachalam et al. entitled “Positive Electrode Materialfor Lithium Ion Batteries Having a High Specific Discharge Capacity andProcesses for the Synthesis of these Materials”, and published U.S.patent application 2010/0151332A (the '332 application) to Lopez et al.entitled “Positive Electrode Materials for High Discharge CapacityLithium Ion Batteries”, both incorporated herein by reference.

The positive electrode material can be advantageously synthesized byco-precipitation and sol-gel processes detailed in the '160 patent andthe '332 application. In some embodiments, the positive electrodematerial is synthesized by precipitating a mixed metal hydroxide orcarbonate composition from a solution comprising +2 cations wherein thehydroxide or carbonate composition has a selected composition. The metalhydroxide or carbonate precipitates are then subjected to one or moreheat treatments to form a crystalline layered lithium metal oxidecomposition. A carbonate co-precipitation process described in the '332application gave desired lithium rich metal oxide materials havingcobalt in the composition and exhibiting the high specific capacityperformance with superior tap density. The '160 patent and '332application also describe the effective use of metal fluoride coatingsto improve performance and cycling.

It is found that for many positive electrode active materials a coatingon the material can improve the performance of the resulting batteries.Suitable coating materials, which are generally believed to beelectrochemically inert during battery cycling, can comprise metalfluorides, metal oxides, metal non-fluoride halides or metal phosphates.The results in the Examples below are obtained with materials coatedwith metal fluorides.

For example, the general use of metal fluoride compositions as coatingsfor cathode active materials, specifically LiCoO₂ and LiMn₂O₄, isdescribed in published PCT application WO 2006/109930A to Sun et al.,entitled “Cathode Active Material Coated with Fluorine Compound forLithium Secondary Batteries and Method for Preparing the Same,”incorporated herein by reference. Improved metal fluoride coatings withappropriately engineered thicknesses are described in published U.S.patent application 2011/0111298 to Lopez et al, (the '298 application)entitled “Coated Positive Electrode Materials for Lithium IonBatteries,” incorporated herein by reference. Suitable metal oxidecoatings are described further, for example, in published U.S. patentapplication 2011/0076556 to Karthikeyan et al. entitled “Metal OxideCoated Positive Electrode Materials for Lithium-Based Batteries”,incorporated herein by reference. The discovery of non-fluoride metalhalides as desirable coatings for cathode active materials is describedin published U.S. patent application 2012/0070725 to Venkatachalam etal., entitled “Metal Halide Coatings on Lithium Ion Battery PositiveElectrode Materials and Corresponding Batteries,” incorporated herein byreference. The synthesis approaches along with the coating provide forsuperior performance of the materials with respect to capacity as wellas cycling properties. The desirable properties of the active materialalong with the use of desirable anode material described herein providefor improved battery performance.

Performance

The processed silicon suboxide-graphitic carbon composite materials canbe effectively incorporated into silicon based batteries. To examine thegeneral performance properties of the materials, electrodes formed withthe composites can be assembled into a battery with lithium foil counterelectrodes. In general though, the composites are particularly desirablewith respect to use as a negative electrode in a lithium ion battery,for example, with a high capacity lithium rich metal oxide positiveelectrode active material. The general construction of lithium basedbatteries is outlines above, and specific testing batteries aredescribed more specifically in the Examples below.

With respect to high capacity silicon based active materials, design ofparticular electrode parameters can be significant with respect toobtaining desirable performance parameters. The general principles ofelectrode design for high capacity silicon based materials has beenelucidated as described in copending U.S. patent application Ser. No.13/777,722 to Masarapu et al., now U.S. Pat. No. 9,780,358, entitled“Battery Designs With High Capacity Anode Materials and CathodeMaterials,” incorporated herein by reference. In general, with existingelectrode designs to obtain good cycling, the density of the anode withrespect to the active material is generally from about 0.4 g/cc (gramsper cubic centimeter) to about 1.3 g/cc. Loading in an electrode relatesto the total amount of active material, and the loading and densityinformation correspondingly provide information on the electrodethickness. The results in the examples suggest that the high ratedischarge capacities can be reduced for thicker electrodes, i.e.,electrodes with a higher loading. In general, the loading levels can beat least about 1.5 mg/cm², in further embodiments from about 1.6 mg/cm²to about 5.5 mg/cm² and in some embodiments from about 1.8 mg/cm² toabout 3.5 mg/cm². A person of ordinary skill in the art will recognizethat additional ranges of electrode parameters within the explicitranges above are contemplated and are within the present disclosure.

Electrodes formed with the silicon based materials can be tested againsta lithium foil electrode to evaluate the capacity and the IRCL.Specifically, batteries assembled with a lithium foil electrode arecycled with the silicon based electrode functioning as a positiveelectrode (cathode) and the lithium foil functions as the negativeelectrode (anode). The batteries with a lithium foil electrode can becycled over a voltage range, for example, from 0.005V to 1.5 V at roomtemperature. Alternatively, batteries can be formed with a positiveelectrode comprising a layered-layered lithium rich metal oxide in whichthe silicon oxide based electrode is then the negative electrode, andthe battery can then be cycled between 4.5 volts and 1.0 volt at roomtemperature after initial activation in the first cycle, or anothervoltage window can be used. For the batteries with a lithium metaloxide-based positive electrode, the first cycle can be charged anddischarged at a rate of C/20 and subsequent cycling can be at a rate ofC/3 unless specified otherwise with charging at C/3, although otherrates and variation of rates with cycle number can be selected fortesting the battery performance. The specific discharge capacity is verydependent on the discharge rate. The notation C/x implies that thebattery is discharged at a rate to fully discharge the battery to theselected voltage minimum in x hours.

For the batteries formed with a lithium metal oxide based positiveelectrode, the specific capacity of the battery can be evaluated againstthe weights of either anode active material or cathode active material,which involved division of the capacity by the respective weights. Ifsupplemental lithium is included in the battery, the weight of thenegative electrode active material can include the weight of thesupplemental lithium since the supplemental lithium contributes to thenegative electrode capacity. Using a high capacity positive electrodeactive material, the overall benefits of using a high capacity siliconoxide based negative electrode active material becomes even morebeneficial. Based on the capacity of the battery, the specificcapacities can be obtained by dividing the respective weight of theactive materials in each electrode. It can be desirable to have highspecific capacities for both electrodes.

In general, it can be desirable for the negative electrode to have aspecific discharge capacity at a rate of C/20 that is at least about 800mAh/g, in additional embodiments at least about 1200 mAh/g, in someembodiment at least about 1400 mAh/g, in other embodiments at leastabout 1500 mAh/g and in further embodiments at least about 1550 mAh/g ata rate of C/20 against lithium from 0.005V to 1.5V. When lithium isextracted from the silicon based composite against lithium an externalvoltage is applied, but this is termed discharge for consistency withcorresponding capacities in a lithium ion battery. In some embodiments,the specific discharge capacity at the tenth cycle of at least about 700mAh/g, in other embodiments at least about 1000 mAh/g, in otherembodiments at least about 1250 mAh/g, in further embodiments at leastabout 1300 mAh/g, in some embodiments at least about 1350 mAh/g, inadditional embodiments at least about 1375 mAh/g, and in someembodiments at least about 1400 mAh/g at a discharge rate of C/3 whencycled between 1.5V and 0.005V against a lithium counter electrode basedon the anode active weight. Comparable specific capacities can beobtained in a lithium ion battery with a high capacity lithium richmetal oxide cycled between 4.5V and 1.0V. Depending on the specificsilicon based active material, the lower voltage cutoff in the lithiumion battery can be selected to be 2.5V, 2.0V, 1.5V, 1.0V or 0.5V. Ingeneral, the lower voltage cutoff can be selected to extract a selectedportion of the electrode capacity from about 92% to about 99%, and infurther embodiments from about 95% to about 98% of the total capacity ofthe positive electrode. In some embodiments, particularly high values ofspecific capacity have been achieved with stable cycling to at least 300cycles. In some embodiments, the material can exhibit a 50th cycledischarge capacity at a discharge rate of C/3 at least about 87% and infurther embodiments at least about 90% of the 5th cycle dischargecapacity when discharged from 1.5V to 0.005V at a rate of C/3 against alithium metal counter electrode. A person of ordinary skill in the artwill recognize that additional ranges of performance values within theexplicit ranges above are contemplated and are within the presentdisclosure.

As noted above, it can be desirable to have a relatively high specificcapacity for both electrodes when the positive electrode comprises alithium rich metal oxide, and the battery can exhibit at a dischargerate of C/3 at the 50th cycle a positive electrode specific capacity ofat least about 150 mAh/g and a negative electrode specific capacity ofat least about 750 mAh/g, in further embodiments a positive electrodespecific capacity of at least about 160 mAh/g and a negative electrodespecific capacity of at least about 800 mAh/g, and in additionalembodiments a positive electrode specific capacity of at least about 170mAh/g and a negative electrode specific capacity of at least about 1000mAh/g, when discharged between 4.5V and 1.0V. The batteries with lithiumrich metal oxides and silicon oxide based materials can exhibitdesirable cycling properties, and in particular the batteries canexhibit a discharge capacity decrease of no more than about 15 percentat the 50th discharge cycle relative to the 7th discharge cycle and infurther embodiments no more than about 10 percent when discharged at arate of C/3 from the 7th cycle to the 50th cycle. In some embodiments,the batteries further include supplemental lithium to reduce theirreversible capacity loss and to stabilize the cycling of lithium richmetal oxides.

EXAMPLES

To test various silicon based electrode compositions, batteries wereconstructed and tested. In some of the Examples, electrodes formed withthe silicon based electrode composition were tested in batteries againstlithium foil as the counter electrode. Other coin cell batteries wereformed with high capacity positive electrodes with the high capacitysilicon based electrodes at a selected electrode balance withsupplemental lithium to compensate for at least some irreversiblecapacity loss. The general procedure for formation of the coin batteriesis described in the following discussion. The batteries were cycled overa relevant voltage range to evaluate performance. The individualexamples below describe formulation of a silicon based negativeelectrode active material, and the performance results from thebatteries. The batteries with silicon based electrode described hereinin general were cycled by charging from the open circuit voltage to 4.6Vand discharging between 4.6V and 1.5V in the first formation cycle andbetween 4.5V and 1.5V for subsequent cycles in the cycle testing forbatteries with high capacity manganese rich (HCMR®) positive counterelectrode or between 0.005V and 1.5V for batteries with lithium foilcounter electrode. With the lithium foil counter electrode used fortesting purposes, the electrode with the silicon based materialfunctions as the positive electrode for these batteries, but theelectrode with the silicon based material may still be referred to asthe “negative electrodes” for simplicity since in a commercial batterythese electrodes would be used as negative electrodes with a lithiumintercalation composition in the positive electrode. The batteries weredischarged at a rate of C/20, C/10, C/5, and C/3 for the 1st and 2ndcycles, for the 3rd and 4th cycles, for the 5th and 6th cycles and forsubsequent cycles, respectively. All percentages reported in theexamples are weight percents unless explicitly indicated otherwise.

Electrodes formed with the silicon based material were formed fromspecific composite materials, which are described further below. Ingeneral, a powder of the silicon based composite active material, i.e.,the processed silicon suboxide-graphitic carbon composite, was mixedthoroughly with an electrically conductive carbon additive, such as ablend of acetylene black (Super P® from Timcal, Ltd., Switzerland) witheither graphite or carbon nanotubes, to form a homogeneous powdermixture. Separately, polyimide binder was mixed withN-methyl-pyrrolidone (“NMP”) (Sigma-Aldrich) and stirred overnight toform a polyimide-NMP solution. The homogenous powder mixture was thenadded to the polyimide-NMP solution and mixed for about 2 hours to formhomogeneous slurry. The slurry was applied onto a copper foil currentcollector to form a thin, wet film and the laminated current collectorwas dried in a vacuum oven to remove NMP and to cure the polymer. Thelaminated current collector was then pressed between rollers of a sheetmill to obtain a desired lamination thickness. The dried laminatecontained at least 75 wt % processed silicon suboxide-graphitic carboncomposite active material and at least 2 wt % polyimide binder. Theresulting electrodes were assembled with either a lithium foil counterelectrode or with a counter electrode comprising a lithium metal oxide(LMO), such as high capacity manganese rich (HCMR®) lithium metal oxidematerial as synthesized in the '160 patent, the '332 application, andthe '534 patent referenced above.

The appropriate examples below use HCMR® positive material approximatelydescribed by the formula xLi₂MnO₃.(1−x)Li Ni_(u)Mn_(v)Co_(w)O₂ wherex=0.5. The lithium rich positive electrode active materials arediscussed in detail in the '534 patent cited above. The positiveelectrode active material had an AlF₃ protective nanocoating. Positiveelectrodes were formed from the synthesized HCMR® powder by initiallymixing it thoroughly with conducting carbon black (Super P™ from Timcal,Ltd, Switzerland) and either graphite (KS 6™ from Timcal, Ltd) or carbonnanotubes to form a homogeneous powder mixture. Separately,Polyvinylidene fluoride PVDF (KF1300™ from Kureha Corp., Japan) wasmixed with N-methyl-pyrrolidone (Sigma-Aldrich) and stirred overnight toform a PVDF-NMP solution. The homogeneous powder mixture was then addedto the PVDF-NMP solution and mixed for about 2 hours to form homogeneousslurry. The slurry was applied onto an aluminum foil current collectorto form a thin, wet film and the laminated current collector was driedin vacuum oven at 110° C. for about two hours to remove NMP. Thelaminated current collector was then pressed between rollers of a sheetmill to obtain a desired lamination thickness. The dried positiveelectrode comprised at least about 75 weight percent active metal oxide,at least about 1 weight percent graphite, and at least about 2 weightpercent polymer binder. Positive electrodes using HCMR® positiveelectrode active material are generally referred to as HCMR® electrodes.

For batteries with the lithium foil counter electrodes, the electrodeswere placed inside an argon filled glove box for the fabrication of thecoin cell batteries. Lithium foil (FMC Lithium) having thickness ofroughly 125 micron was used as a negative electrode. A conventionalelectrolyte comprising carbonate solvents, such as ethylene carbonate,diethyl carbonate and/or dimethyl carbonate, was used. A trilayer(polypropylene/polyethylene/polypropylene) micro-porous separator (2320from Celgard, LLC, NC, USA) soaked with electrolyte was placed betweenthe positive electrode and the negative electrode. Some additionalelectrolyte was added between the electrodes. The electrodes were thensealed inside a 2032 coin cell hardware (Hohsen Corp., Japan) using acrimping process to form a coin cell battery. The resulting coin cellbatteries were tested with a Maccor cycle tester to obtaincharge-discharge curve and cycling stability over a number of cycles.All batteries were electrochemically characterized in the range of 0.005to 1.5V (2 cycles at C/20, 2 cycles at C/10, 2 cycles at C/5, the restat C/3).

For batteries with the HCMR® counter electrodes, the silicon oxide basedelectrode and the HCMR® electrode were placed inside an argon filledglove box. An electrolyte was selected to be stable at high voltages,and appropriate electrolytes with halogenated carbonates, e.g.,fluoroethylene carbonate are described in copending U.S. patentapplication Ser. No. 13/325,367 to Li et al., now published U.S. patentapplication 2013/0157147, entitled “Low Temperature Electrolyte for HighCapacity Lithium Ion Batteries,” incorporated herein by reference. Basedon these electrodes and the high voltage electrolyte, the coin cellbatteries were completed with separator and hardware as described abovefor the batteries with the lithium foil electrode.

Some of the batteries fabricated from a silicon based negative electrodeand a HCMR® positive electrode can further comprise supplementallithium. In particular, a desired amount of SLMP® powder (FMC Corp.,stabilized lithium metal powder) was loaded into a vial and the vial wasthen capped with a mesh comprising nylon or stainless steel with a meshsize between about 40 μm to about 80 μm. SLMP® (FMC corp.) was thendeposited by shaking and/or tapping the loaded vial over a formedsilicon based negative electrode. The coated silicon based negativeelectrode was then compressed to ensure mechanical stability.

Batteries fabricated from a silicon based negative electrode and a HCMR®positive electrode can be balanced to have excess negative electrodematerial. The balancing was based on the ratio of the first cyclelithium insertion capacity of the silicon based negative electrode tothe total available lithium in the battery which is the sum of theoxidation capacity of the supplemental lithium and the theoreticalcapacity of the HCMR® positive electrode. In particular, for a givensilicon based active composition, the insertion and extractioncapacities of the silicon based composition can be evaluated in abattery setting. For example, a battery that has a positive electrodecomprising the silicon based active material with a counter lithium foilnegative electrode can be constructed. The insertion and extractioncapacities of the silicon based composition in the electrode equals tothe first cycle battery capacity measured when lithium isintercalated/alloyed to the silicon based electrode to 5 mV andde-intercalated/de-alloyed to 1.5V at a rate of C/20. For the fullbattery with the lithium metal oxide based positive electrode, values ofthe excess negative electrode balance are provided in the specificexamples below. For batteries containing supplemental lithium, theamount of supplemental lithium was selected to approximately compensatefor the irreversible capacity loss of the negative electrode.

Example 1—Formation of Processed Silicon Suboxide Composites

This Example demonstrates the effects of milling process parameters onthe composition and structure of processed silicon suboxide compositesformed by high energy milling of SiO with either wet milling or drymilling.

To demonstrate the effect of milling parameters on the composition ofprocessed silicon suboxide composites, 4 samples (samples 1-4) wereformed. For each sample, an appropriate amount of SiO powder (SigmaAldrich) was added to a 500 ml zirconia jar along with zirconia millingballs. For samples 1 and 2, an appropriate amount of ethanol as a liquidmedia was also added to the zirconia jar. The jars were then sealed andplaced into a high energy planetary ball mill. The SiO was milled at aspeed of between about 150 rpm and about 400 rpm, and between about 1hour and about 30 hours, with 1 hr≤t₁<t₂<t₃<t₄<t₅<t₆<t₇<t₈<t₉≤30 hrs.After milling, the wet samples were dried. X-ray diffraction (XRD)analysis was then performed on each of the 4 samples as well as on areference sample of powdered SiO. FIG. 2 is a plot of the scatteringangle versus intensity obtained by XRD analysis of each of the samples.The bottom panel of FIG. 2 shows an XRD plot of crystalline silicon. Asused herein, a milling using liquid media is referred to as “wet”milling and a milling without using liquid media is referred to as “dry”milling.

FIG. 2 demonstrates that the presence and relative amount of crystallinesilicon in the processed silicon suboxide composite formed duringmilling can be controlled by varying milling process parameters. Withrespect to milling time and speed, comparison of samples 1 and 2 (bothwet) and samples 3 and 4 (both dry) demonstrate that increased millingspeed and milling time resulted in a greater amount of crystallineformed during milling. With respect to milling type, comparison of thex-ray diffraction plots of sample 2 (wet) and sample 3 (dry)demonstrates that more elemental silicon was crystallized from the SiOmatrix during the dry milling process relative to the wet millingprocess under similar milling conditions and that zirconia contaminationfrom the milling balls was present in wet milled samples withsignificant amounts of crystalline silicon.

To examine the effect of processing parameters on the structure ofprocessed silicon suboxide composites, 14 more samples (samples 5-18)were formed similarly as described above. The samples were wet milled ordry milled at a speed between about 200 rpm and about 350 rpm and forbetween about 1 hour and about 30 hours. After formation, the sampleswere then analyzed to determine the average surface area and volumeaverage secondary particle size (D50). Surface areas were obtained fromBET adsorption cross section measurements performed on the samples. Meanparticles sizes were obtained from dynamic light scattering (DLS)measurements performed on the samples. A portion of dry sample powderwas placed into the measuring device (Saturn Digisizer™, Micromeritics),which added isopropanol and sonicated to disperse the particles.

TABLE 3 Sample Milling Speed Time Surface Area D50 Number Type (RPM)(hours) (m²/g) (μm) 5 Dry 350 t₉ 13.5 N/A 6 Dry 350 t₈ 11.5 0.46 7 Dry350 t₇ 11 N/A 8 Dry 350 t₅ 12.6 N/A 9 Dry 300 t₂ 9.2 1.83 10 Dry 300 t₄10.7 0.49 11 Dry 300 t₅ 14.7 0.49 12 Dry 300 t₆ 14.4 0.44 13 Wet 300 t₁3.9 7.1  14 Wet 300 t₂ 4.8 6.6  15 Wet 300 t₄ 9.7 0.45 16 Wet 200 t₂ 1.68.8  17 Wet 200 t₃ 5.8 0.67 18 Wet 200 t₅ 6.2 0.64

The results presented in Table 3 demonstrate that, in general, longermilling times resulted in samples having smaller mean processed siliconsuboxide particle sizes and larger surface areas. Comparison of drymilled samples 9-12 demonstrates that continued milling over time periodgreater than 2 hours reduced the mean processed silicon suboxideparticle size from 1.83 μm to 0.44 μm and the surface area of thesamples from 9.2 m²/g to 14.4 m²/g. Likewise, comparison of wet milledsamples 13-15 demonstrates that continued milling over time periodgreater than an hour reduced the mean processed silicon suboxideparticle size from 7.1 μm to 0.45 μm and increased the surface area ofthe samples from 3.9 m²/g to 9.7 m²/g. Similarly, comparison of wetmilled samples 16-18 demonstrates that continued milling over timeperiod greater than 2 hours reduced the mean processed silicon suboxideparticle size from 8.8 μm to 0.64 μm and increased the surface are ofthe samples from 1.6 m²/g to 6.2 m²/g.

The results in Table 3 also demonstrate that increased milling rateresulted in samples having a larger surface area. Comparison of drysamples 8 and 11 demonstrates that increasing the milling rate from 300(sample 11) rpm to 350 rpm (sample 8) decreased the surface area thesamples from 14.7 m²/g (sample 11) to 12.6 m²/g (sample 8). Similarly,comparison of wet samples 14 and 16 demonstrates that increasing themilling rate from 200 rpm (sample 16) to 300 rpm (sample 14) increasedthe surface area of the samples from 1.6 m²/g (sample 16) to 4.8 m²/g(sample 14).

With respect to milling type, the results tabulated in Table 3 indicatethat wet milling resulted in samples having a smaller surface area.Comparison of samples 9 (dry) and 14 (wet) demonstrate that wet millingreduced the surface area from 9.2 m²/g (sample 9) to 4.8 m²/g (wet) andcomparison of samples 10 (dry) and 15 (wet) demonstrate that wet millingreduced the surface area from 10.7 m²/g (sample 10) to 9.7 m²/g (sample15). However, with respect to mean processed silicon suboxide particlesize, no definitive trend was observed for the samples tested. Inparticular, comparison of samples 9 and 14 demonstrates that wet millingincreased the mean particle size from 1.83 μm (sample 9) to 6.2 μm(sample 14) and comparison of samples 10 and 15 demonstrates that wetmilling slightly decreased the mean particle size from 0.49 μm (sample10) to 0.45 μm (sample 15). In comparing the surface area and particlessizes for wet milling and dry milling, dry milling resulted in highervalues of surface area for similar D50 particle sizes, suggesting thatthe dry milled materials are more porous.

Example 2—Effect of Milling Parameters on the Composition and Structureof Processed Silicon Suboxide-Graphitic Carbon Composites

This Example demonstrates the effects of milling parameters on thecomposition and structure of processed silicon suboxide-graphitic carboncomposites. A first set of results is presented which demonstrates theeffects of milling time on the composition of processed siliconsuboxide-graphitic carbon composites. A second set of results in thenpresented demonstrating the effects of various milling parameters,including milling time, on the structure of processed siliconsuboxide-graphitic carbon composites. This Example further demonstratesthe formation of graphene sheets within composites formed from themilling of the processed silicon suboxide with graphitic carbon.

To demonstrate the effect of milling time on composition, 4 samples(samples 23-26 of Table 3) were analyzed by x-ray diffraction. FIG. 3 isa graph showing plots of scattering angle versus intensity obtained fromXRD analysis of samples 23-26. The lower two panels of FIG. 3 displaythe XRD spectra for silicon and graphite. FIG. 3 demonstrates thatsamples having longer milling times had lesser amounts of graphite,suggesting that longer milling times resulted in larger amounts ofgraphite being converted to graphene. Also, longer milling times seemsto result in the loss of crystalline silicon while some graphiteremained, while shorter milling time did not seem to change the amountof crystalline silicon. The results suggest that excessive milling toconvert more graphite to graphene can alter silicon active phase in apossibly adverse way.

To demonstrate the effect of various milling processing parameters onprocessed silicon suboxide-graphitic carbon composite structure, samples23-34 were formed as described above. For samples 23-28, processedsilicon suboxide composites were formed with SiO wet milling or drymilling at 300 rpm or 350 rpm for 1 hour or 15 hours. Samples 29-34 wereprepared from the processed silicon suboxide composite samples 13-18.Processed silicon suboxide-graphitic carbon composite samples 23-34 wereformed from the processed silicon suboxide composites by SiO/graphitemilling at 200 rpm or 300 rpm for 0.5 hours to 4 hours (0.5hrs≤s₁<s₂<s₃<s₄≤4 hrs), to form the composite samples. Table 4 displaysthe process parameters and structural characteristics of the samples.

TABLE 4 SiO Milling Parameters Processed SiO/Graphite Milling ParametersMilling Speed Time Milling Speed Time SA, D50 Sample Type (RPM) (Hours)Type (RPM) (Hours) (m2/g) (μm) 23 dry 350 t₈ dry 300 s₁ 17.4 3.5 24 dry350 t₈ dry 300 s₂ 20.6 1.5 25 dry 350 t₈ dry 300 s₃ 24.1 1.5 26 dry 350t₈ dry 300 s₄ 28 1.3 27 dry 350 t₈ dry 200 s₂ 16.2 1.5 28 dry 350 t₈ dry200 s₃ 20.4 1 29 wet 300 t₁ dry 300 s₃ 16.7 0.91 30 wet 300 t₂ dry 300s₃ 17.0 0.74 31 wet 300 t₄ dry 300 s₃ 17.6 0.59 32 wet 200 t₂ dry 300 s₃17.4 0.98 33 wet 200 t₃ dry 300 s₃ 12.6 0.53 34 wet 200 t₅ dry 300 s₃17.4 0.67

Referring to Table 4, increased SiO/graphite milling times generallyresulted in processed silicon suboxide-graphitic carbon compositeshaving smaller mean particle diameters and increased surface areas. Forsamples 23-26, the mean particle diameter generally decreased (form 3.5μm to 1.3 μm) and the surface area increased (from 17.4 m²/g to 28 m²/g)when the milling time was increased from 0.5 hours to 4 hours. Notably,increasing the milling time from sample 24 to sample 25 did not appearto further reduce the mean particle size but the surface area wasfurther increased from 20.6 m²/g (sample 24) to 24.1 m²/g (sample 25).Similarly, for samples 27 and 28, as the processed SiO/Graphite millingtime increased from sample 27 to sample 28, the mean particle diameterdecreased from 1.5 μm to 1 μm and the surface area increased from 16.2m²/g to 20.4 m²/g. Additionally, Table 4 demonstrates that reducedmilling speeds generally resulted in samples having reduced surfaceareas and reduced mean particle diameters. Comparison of sample 24 withsample 27 and comparison of sample 25 with sample 28 demonstrates thatreduced milling speed (samples 27 and 28) resulted in samples 27 and 28having lower surface areas and similar or smaller mean particlediameters relative to samples 24 and 25, respectively. With respect tothe effect of SiO wet milling on the formation of the composites, Table4 demonstrates that wet milling of SiO prior to milling with graphiteproduced a processed silicon suboxide-graphitic carbon composite sample(sample 29) having a smaller surface area and mean particle diameterrelative to the analogous processed silicon suboxide-graphitic carboncomposite sample (sample 25) formed by starting with dry milled SiO,which is again consistent with a less porous material being formedduring the wet milling of SiO.

The effect of SiO milling parameters on processed siliconsuboxide-graphitic carbon composites can be seen by comparing samples13-18 in Table 3 with samples 29-34 (made from samples 13-18) in Table3. Referring to Tables 3 and 4, samples prepared with longer SiO millingtimes generally had smaller processed silicon suboxide-graphitic carboncomposite mean particle sizes. As explained above with respect tosamples 13-18, longer SiO milling times generally translated intosamples have smaller processed silicon suboxide mean particle sizes.Table 4 demonstrates for most samples tested, smaller processed siliconsuboxide mean particle sizes generally translated into small processedsilicon suboxide-graphitic carbon mean particle sizes. Although, it isnoted that sample 33 (processed silicon suboxide mean particle size of0.67 μm, see Table 3) had a smaller processed silicon suboxide-graphiticcarbon mean particle size than sample 34 (processed silicon suboxidemean particle size of 0.64). With respect to surface area, again, withthe exception of sample 33, longer processed silicon suboxide millingtimes resulted in larger increased composite surface areas, due to thesmaller mean particle sizes.

To demonstrate the structure of a representative composite, a processedsilicon suboxide-graphitic carbon composite sample was formed (sample25) as described above with SiO dry milling. FIGS. 4 and 5A and 5B showtransmission electron microscopy (TEM) images of sample 25. Referring tothe figures, the TEM images clearly show embedded Si—SiO_(x) particlesin exfoliated graphene sheets. In particular, the TEM images demonstrateexfoliation of graphite to form graphene sheets and the formation ofnanoparticles from micron sized SiO, during milling. The TEM images alsoshow that SiO and Si particles are embedded between the graphene sheets.

To investigate the local composition of a representative processedsilicon suboxide-graphitic carbon composites, energy dispersive X-rayspectroscopy (EDS) analysis was performed on sample 25 in conjunctionwith the TEM analysis. FIG. 6 is a cropped reproduction of the TEM imagedisplayed in FIG. 4 and denotes the locations at which EDS spectra wereobtained. Table 5 displays the results of the EDS analysis on sample 25in atomic percent of the constituent elements. Referring to Table 5 andFIG. 6 , EDS analysis demonstrates that the sample areas correspondingto spectra 1 and 2 comprise SiO without and with graphene coverage,respectively. Furthermore, Table 5 and FIG. 6 are consistent with thesample area with spectrum 3 corresponding to elemental Si with graphenecoverage. To obtain a visualization of the local composition of sample25, two dimensional EDS mappings were obtained and are displayed inFIGS. 7A-7D. FIG. 7A displays a portion of the TEM image displayed inFIG. 6 and corresponds to the sample area in which EDS analysis wasperformed to obtain elemental mappings. FIGS. 7B-7D corresponding to EDSmappings of carbon, oxygen and silicon, respectively, onto the twodimensional sample area displayed in FIG. 7A. In FIGS. 7B-7D, lighterareas correspond to higher atomic concentrations and darker areascorrespond to lower atomic concentrations. FIG. 7B (carbon analysis)demonstrates the presence of the graphene sheet formed from theexfoliation of graphite during milling. FIGS. 7C (oxygen analysis) and7D (silicon analysis) demonstrate the presence of SiO as well as SiOparticles and Si particles in the processed silicon suboxide-graphiticcarbon composite of sample 25.

TABLE 5 Carbon Oxygen Silicon Compound/ Location (at %) (at %) (at %)Element Spectrum 1 44.71 28.44 26.85 SiO Spectrum 2 71.83 15.28 12.9 SiOSpectrum 3 80.88 4.67 14.45 Si

Example 3—Effect of Milling Parameters on the Performance of BatteriesComprising Processed Silicon Suboxide-Graphitic Carbon Electrodes

This Example demonstrates the effects of milling parameters on theperformance of batteries comprising processed silicon suboxide-graphiticcarbon electrodes.

To demonstrate the effect of milling parameters, 13 batteries (batteries1-13) were fabricated. Batteries 1-7 were fabricated samples 23-29 (SiOdry milling), respectively, and batteries 8-13 were fabricated fromsamples 30-35 (SiO wet milling), respectively. Each battery had anelectrode comprising a processed silicon suboxide-graphitic carboncomposite and a lithium foil counter electrode. After battery assembly,the batteries were cycled as described above for at least 50 cycles, andthe corresponding charge and discharge capacities were measured. Table 6displays the milling parameters, initial battery performance and cyclingperformance of each of the batteries. It should be noted that forbatteries with a lithium foil counter electrode, the transfer of lithiumions through the electrolyte and subsequent intercalation into theprocessed silicon suboxide-graphitic carbon composite electrode is aspontaneous process, so that the silicon based active material functionsas the cathode.

The results in Table 6 indicate the effect of milling parameters on thecycling performance of batteries formed from the processed siliconsuboxide-graphitic carbon composite samples in Table 4. Referring toTable 6, for batteries formed using a processed SiO/Graphite millingspeed of 300 rpm (batteries 1-4, formed from samples 23-26), increasedcycling performance was observed with increased milling times up to 2hour. Referring to the results for batteries 1-3, increased millingtimes resulted in lower first cycle IRCL and increased C/3 specificdischarge capacities. However, batteries 2 and 3 (t₂ and t₃ millingtimes, respectively) had slightly decreased capacity retention after 50cycles relative to battery 1 (t₁ milling time). For battery 4, which wasalso formed using a processed SiO/Graphite milling speed of 300 rpm butusing a corresponding milling time of t₄, battery performance wasgenerally not improved relative to batteries 1-3. In particular, whilebattery 4 had a lower first cycle IRCL relative to batteries 1-3,battery 4 had the lowest C/3 specific discharge capacity as well a thelowest capacity retention after 50 cycles relative to batteries 1-3.Notably, that battery 4 was formed from sample 26, which had the highestsurface area relative to samples 23-25 (used to form batteries 1-3,respectively).

TABLE 6 1st Cycle 1st Cycle Charge Discharge Discharge % Cap. CapacityCapacity capacity Retained Battery at C/20 at C/20 IRCL at C/3 after 50Loading, Density Peel Number (mAh/g) (mAh/g) (%) (mAh/g) cycles (mg/cm²)(g/cc) Test 1 2409 1579 35 1431 85 2.7 0.83 N/A 2 2432 1609 34 1499 832.5 0.8 N/A 3 2407 1630 32 1559 83 2.5 0.8 0.2 4 2283 1522 33 1326 752.5 0.77 0.48 5 2604 1631 37 1431 81 2.3 0.6 0.29 6 2644 1724 35 1426 872.1 0.6 0.23 7 2543 1661 35 1455 91 2.5 0.5 0.2 8 2364 1574 33 1349 924.4 0.82 9 2264 1520 33 1182 82 4.2 0.92 10 2308 1807 28 1209 77 4.00.81 11 2259 1525 33 1194 86 4.5 0.71 12 2380 1574 34 1274 80 3.6 0.8113 2365 1590 33 1254 80 3.8 0.85

For processed SiO/Graphite milling speeds at 200 rpm (batteries 5 and 6formed from samples 27 and 28), increased milling times increased thefirst cycle IRCL and increased capacity retention after 50 cycles. TheC/3 specific discharge capacities of batteries 5 and 6 were similar.Furthermore, with respect to processed SiO/Graphite milling speed,comparison of battery 2 (300 rpm) with battery 5 (200 rpm) andcomparison of battery 3 (300 rpm) with battery 6 (200 rpm) demonstratethat decreased milling speed resulted in batteries having a higher firstcycle IRCL and lower C/3 specific discharge capacities. However, battery2 had a higher capacity retention after 50 cycles relative to battery 5,while battery 3 had a lower capacity retention after 50 cycles relativeto battery 6.

With respect to the effect of SiO wet milling on battery performance,comparison of batteries 7-9 (wet milling of SiO) with batteries 2-4 (drymilling of SiO) indicates the batteries fabricated with SiO wet millinghad smaller C/20 and C/3 charge/discharge capacities and similar firstcycle irreversible capacity losses. However, the batteries fabricatedwith SiO wet milling had somewhat improved capacity retention after 50cycles in some embodiments relative to the batteries formed with SiO drymilling. The effect of SiO milling time on capacity on batteriesprepared with SiO wet milling can be seen by comparison of batteries13-15 and 16-17 in Table 6. The table reveals that for a given SiOmilling rate, for the samples tested, increased SiO milling timesgenerally resulted in lower or similar capacity retention.

Example 4—Effect of Graphitic Carbon Concentrations on the Structure ofProcessed Silicon Suboxide-Graphitic Carbon Composites and thePerformance of Batteries Made Therefrom

This Example demonstrates the effect of varying the SiO and graphiteconcentrations on the structure of processed silicon suboxide-graphiticcarbon composites and the ultimate effects on the cycling performance ofbatteries made from those composites. The effect of electrode loading isalso explored.

To demonstrate the effect graphitic carbon concentrations on compositestructure, samples 35-38 were prepared as described above with theamount of graphite being varied. Processed SiO was formed by dry millingSiO at for t₈ hours, and a processed silicon suboxide-graphitic carboncomposite was formed by milling the corresponding processed siliconsuboxide composite with graphite at 300 rpm for t₃ hours. The relativeconcentration of SiO to graphite was different for each sample. To testcycling performance, batteries 14-17 were fabricated as described abovewith electrodes formed from samples 35-38, respectively, and lithiumfoil counter electrodes. Tables 7 and 8 display the sample millingparameters and structural characteristics and battery performanceresults.

TABLE 7 SiO:Gr Surface Median (weight Speed Time Area, Particle size,Sample ratio) (rpm) (hours) (m2/g) microns 35 90:10 300 t₃ 24.1 1.5 3691:09 300 t₃ 24.3 N/A 37 92:08 300 t₃ 24.4 N/A 38 95:05 300 t₃ 19.1 1.5

TABLE 8 1st Cycle 1st Cycle Charge Discharge Discharge % Cap. CapacityCapacity capacity Retained at C/20 at C/20 IRCL at C/3 after 50 Loading,Density Battery (mAh/g) (mAh/g) (%) (mAh/g) cycles (mg/cm²) (g/cc) 142426 1553 36 1033 90 3.4 0.78 15 2461 1641 33 1105 93 2.9 0.70 16 25201688 33 1199 87 3.1 0.74 17 2376 1619 32 1336 68 4.0 N/A

The results in Table 7 indicate that the samples formed with over 5weight percent (wt %) graphite (samples 35-37) had similar surface areaswhile the sample formed with 5 wt % graphite (sample 38) has a smallersurface relative to samples 35-37. With respect to the correspondingbattery performance, Table 8 demonstrates that over 5 wt % graphite(batteries 14-16), batteries with increased weight percent graphitegenerally had smaller first cycle charge and discharge capacities,smaller or similar first cycle IRCL and reduced C/3 specific dischargecapacities. Battery 17, formed using 5 wt % graphite, had the lowestfirst cycle irreversible capacity loss and highest C/3 specificdischarge capacity. However, battery 17 also had the lowest capacityretention after 45 cycles relative to batteries 14-16. Notably, battery16 was formed from sample 38, which had the lowest surface area relativeto samples 35-37 form which batteries 14-16 were formed.

Example 5—Cycling Performance of Batteries Having Electrodes ComprisingProcessed Silicon Suboxide-Graphitic Carbon Composite

This Example demonstrates the cycling performance of batteriescomprising a processed silicon suboxide-graphitic carbon electrodes andlithium foil or lithium metal oxide based counter electrode.

To demonstrate cycling performance, 3 batteries (batteries 18-20) wereformed as described above. Batteries 18 and 19 were formed with lithiumfoil counter electrodes and comprised a commercial silicon compositematerial for the anode electrode (battery 18) or a representative goodcycling processed silicon suboxide-graphitic carbon electrode (battery19). Battery 20 was a formed as a battery that comprised a processedsilicon suboxide-graphitic carbon anode and a high capacity manganeserich cathode, as noted above. To demonstrate performance, batteries18-20 were cycled between 1.5 V and 0.005 V at a charge/discharge rateof C/3 for 55 cycles. Battery 21 was cycled between 4.35 V and 1.5 V for300 cycles were cycled as described above, corresponding to an 80% depthof discharge for battery 14. During the cycling of the batteries, thespecific charge and discharge capacities were measured and the resultsare plotted in FIGS. 8 and 9 .

FIG. 8 is a graph containing plots of specific discharge capacities as afunction of cycle number for batteries 18 and 19. The results in FIG. 8demonstrates that battery formed with the processed siliconsuboxide-graphitic carbon electrode (battery 19) had significantlyimproved cycling performance over the battery formed with the commercialsilicon composite electrode. FIG. 9 is a graph containing plots ofcharge and discharge capacities per unit area of the negative electrodeas a function of cycle number for battery 20. The figure demonstratesbattery 20 had excellent cycling performance over 300 cycles. Inparticular, after the 300th cycle, the capacity retention of battery 20was about 91% percent.

The embodiments above are intended to be illustrative and not limiting.Additional embodiments are within the claims. In addition, although thepresent invention has been described with reference to particularembodiments, those skilled in the art will recognize that changes can bemade in form and detail without departing from the spirit and scope ofthe invention. Any incorporation by reference of documents above islimited such that no subject matter is incorporated that is contrary tothe explicit disclosure herein.

What is claimed is:
 1. A method for forming a composite materialcomprising processed silicon suboxide and graphitic carbon at least aportion of which is in graphene sheets, the method comprising:performing high energy ball milling or jar milling of graphite powderwith processed silicon suboxide material having a BET surface area fromabout 2.5 m²/g to about 20 m²/g and a D50 volume average secondaryparticle size of no more than about 10 microns, to form the compositematerial, wherein the processed silicon suboxide is prepared by highenergy mechanical milling of silicon suboxide prior to blending withgraphite powder to form a blend and performing the high energy ballmilling or jar milling with the blend.
 2. The method of claim 1 whereinthe silicon suboxide is represented by the formula SiO_(x) where0.1≤x≤1.9.
 3. The method of claim 1 wherein the silicon suboxidematerial is processed silicon suboxide formed by high energy mechanicalmilling of silicon suboxide.
 4. The method of claim 3 wherein theprocessed silicon suboxide is substantially free of milling media. 5.The method of claim 1 wherein the high energy ball milling is performedwith zirconium oxide milling beads.
 6. The method of claim 1 wherein theproduct composite material has a BET surface area from about 12 m²/g toabout 35 m²/g and a D50 volume average secondary particle size of nomore than about 5 microns.
 7. The method of claim 1 wherein the productcomposite material comprises graphene sheets visible in micrographs andresidual graphite as determined by x-ray diffraction.
 8. The method ofclaim 1 wherein the product composite material has a discharge capacityof at least about 1200 mAh/g at a rate of C/20 discharged from 1.5V to0.005V against lithium metal, a specific discharge capacity of at leastabout 1250 mAh/g at a rate of C/3 discharged from 1.5V to 0.005V againstlithium metal, and a 50th cycle discharge capacity that is at leastabout 87% of the 5th cycle discharge capacity when cycled againstlithium from 1.5V to 0.005V at a discharge rate of C/3.
 9. The method ofclaim 1 wherein the product composite material has from about 2 weightpercent to about 95 weight percent graphitic carbon.